diff --git a/frontend/src/views/CaptureOverlay.vue b/frontend/src/views/CaptureOverlay.vue
index 0b28a3c..633b75a 100644
--- a/frontend/src/views/CaptureOverlay.vue
+++ b/frontend/src/views/CaptureOverlay.vue
@@ -24,7 +24,8 @@ interface Rect {
   h: number
 }
 
-type Tool = 'pen' | 'rect' | 'ellipse' | 'text'
+type Tool = 'pen' | 'rect' | 'ellipse' | 'text' | 'mosaic-brush' | 'mosaic-rect'
+type MosaicMode = 'brush' | 'rect'
 interface Point {
   x: number
   y: number
@@ -77,6 +78,8 @@ const activeTool = ref<Tool>('pen')
 const activeColor = ref('#ef4444')
 const activeStrokeWidth = ref(3)
 const activeFontSize = ref(20)
+const mosaicMode = ref<MosaicMode>('brush')
+const mosaicBrushWidth = ref(24)
 const textDraft = ref<{
   point: Point
   value: string
@@ -104,6 +107,7 @@ const textDragOriginalPoint = ref<Point | null>(null)
 
 const DEFAULT_TEXT_FONT_SIZE = 20
 const STROKE_WIDTHS = [2, 4, 6]
+const MOSAIC_WIDTHS = [16, 24, 36, 52]
 const FONT_SIZES = [16, 20, 28, 36]
 
 const colors = [
@@ -146,17 +150,18 @@ const sizeLabel = computed(() => {
   return `${Math.round(rect.value.w)} × ${Math.round(rect.value.h)}`
 })
 
-const MARK_TOOLBAR_W = 178
+const MARK_TOOLBAR_W = 212
 const ACTION_TOOLBAR_W = 288
 const TOOLBAR_GROUP_GAP = 8
 
-const toolOrder: Tool[] = ['pen', 'rect', 'ellipse', 'text']
+const toolOrder: Tool[] = ['pen', 'rect', 'ellipse', 'text', 'mosaic-brush', 'mosaic-rect']
 
 const toolSettingsPos = computed(() => {
   if (!leftToolbarPos.value || !rect.value || !activeTool.value) return null
-  const menuW = activeTool.value === 'text' ? 462 : 398
+  const isMosaic = activeTool.value.startsWith('mosaic-')
+  const menuW = isMosaic ? (mosaicMode.value === 'brush' ? 328 : 112) : activeTool.value === 'text' ? 462 : 398
   const menuH = 58
-  const buttonIndex = toolOrder.indexOf(activeTool.value)
+  const buttonIndex = isMosaic ? 4 : toolOrder.indexOf(activeTool.value)
   const buttonCenter = 4 + buttonIndex * 34 + 14
   let x = leftToolbarPos.value.x
   let y = leftToolbarPos.value.y + 44
@@ -432,7 +437,7 @@ function onSelectionMouseDown(e: MouseEvent) {
   draftAnnotation.value = {
     tool: activeTool.value,
     color: activeColor.value,
-    strokeWidth: activeStrokeWidth.value,
+    strokeWidth: activeTool.value === 'mosaic-brush' ? mosaicBrushWidth.value : activeStrokeWidth.value,
     points: [local],
   }
 }
@@ -466,7 +471,7 @@ function onMouseMove(e: MouseEvent) {
       annotation.points[0] = clampTextLocalPoint(next, annotation)
     }
   } else if (dragMode.value === 'annotating' && draftAnnotation.value) {
-    if (activeTool.value === 'pen') {
+    if (activeTool.value === 'pen' || activeTool.value === 'mosaic-brush') {
       draftAnnotation.value.points.push(localPoint(p))
     } else {
       draftAnnotation.value.points = [
@@ -524,6 +529,19 @@ function selectTool(tool: Tool) {
   activeTool.value = tool
 }
 
+function selectMosaic() {
+  activeTool.value = mosaicMode.value === 'brush' ? 'mosaic-brush' : 'mosaic-rect'
+}
+
+function chooseMosaicMode(mode: MosaicMode) {
+  mosaicMode.value = mode
+  selectMosaic()
+}
+
+function chooseMosaicWidth(width: number) {
+  mosaicBrushWidth.value = width
+}
+
 function chooseColor(color: string) {
   activeColor.value = color
   if (textDraft.value) {
@@ -748,6 +766,13 @@ onUnmounted(() => {
       :viewBox="`0 0 ${width} ${height}`"
       preserveAspectRatio="none"
     >
+      <defs>
+        <pattern id="mosaic-preview" width="10" height="10" patternUnits="userSpaceOnUse">
+          <rect width="10" height="10" fill="rgba(71,85,105,.82)" />
+          <rect width="5" height="5" fill="rgba(203,213,225,.82)" />
+          <rect x="5" y="5" width="5" height="5" fill="rgba(148,163,184,.82)" />
+        </pattern>
+      </defs>
       <path :d="maskPath" fill="rgba(0,0,0,0.45)" fill-rule="evenodd" />
       <rect
         v-if="rect"
@@ -811,6 +836,25 @@ onUnmounted(() => {
             {{ annotation.text }}
           </text>
         </template>
+        <polyline
+          v-else-if="annotation.tool === 'mosaic-brush'"
+          :points="annotation.points.map((p) => `${p.x},${p.y}`).join(' ')"
+          stroke="url(#mosaic-preview)"
+          :stroke-width="annotation.strokeWidth || 24"
+          stroke-linecap="round"
+          stroke-linejoin="round"
+          fill="none"
+        />
+        <rect
+          v-else-if="annotation.tool === 'mosaic-rect' && annotation.points.length >= 2"
+          :x="Math.min(annotation.points[0].x, annotation.points[1].x)"
+          :y="Math.min(annotation.points[0].y, annotation.points[1].y)"
+          :width="Math.abs(annotation.points[1].x - annotation.points[0].x)"
+          :height="Math.abs(annotation.points[1].y - annotation.points[0].y)"
+          fill="url(#mosaic-preview)"
+          stroke="rgba(255,255,255,.8)"
+          stroke-width="1"
+        />
       </g>
     </svg>
 
@@ -922,6 +966,21 @@ onUnmounted(() => {
           <path d="M9 19h6" />
         </svg>
       </button>
+      <button
+        class="icon-btn"
+        :class="{ active: activeTool.startsWith('mosaic-') }"
+        title="马赛克标记"
+        aria-label="马赛克标记"
+        :aria-expanded="activeTool.startsWith('mosaic-')"
+        @click="selectMosaic"
+      >
+        <svg viewBox="0 0 24 24" aria-hidden="true">
+          <rect x="4" y="4" width="6" height="6" />
+          <rect x="14" y="4" width="6" height="6" />
+          <rect x="4" y="14" width="6" height="6" />
+          <rect x="14" y="14" width="6" height="6" />
+        </svg>
+      </button>
       <button
         class="icon-btn"
         :class="{ muted: annotations.length === 0 }"
@@ -947,7 +1006,55 @@ onUnmounted(() => {
       }"
       @mousedown.stop
     >
-      <div v-if="activeTool !== 'text'" class="setting-group stroke-group">
+      <template v-if="activeTool.startsWith('mosaic-')">
+        <div class="setting-group mosaic-mode-group" role="group" aria-label="马赛克标记方式">
+          <button
+            class="mode-choice"
+            :class="{ active: mosaicMode === 'brush' }"
+            title="涂抹"
+            aria-label="涂抹马赛克"
+            :aria-pressed="mosaicMode === 'brush'"
+            @click="chooseMosaicMode('brush')"
+          >
+            <svg viewBox="0 0 24 24" aria-hidden="true">
+              <path d="M9 11V5.5a2 2 0 0 1 4 0V10" />
+              <path d="M13 10V8a2 2 0 0 1 4 0v3" />
+              <path d="M17 10a2 2 0 0 1 4 0v4.5c0 4-2.5 6.5-6.5 6.5h-1.2a6 6 0 0 1-4.7-2.3L4 13.2a1.9 1.9 0 0 1 2.8-2.5L9 12.5" />
+            </svg>
+          </button>
+          <button
+            class="mode-choice"
+            :class="{ active: mosaicMode === 'rect' }"
+            title="框选"
+            aria-label="框选马赛克"
+            :aria-pressed="mosaicMode === 'rect'"
+            @click="chooseMosaicMode('rect')"
+          >
+            <svg viewBox="0 0 24 24" aria-hidden="true">
+              <rect x="2.5" y="2.5" width="19" height="19" rx="2" />
+              <rect class="pixel-block" x="6" y="6" width="4" height="4" rx=".5" />
+              <rect class="pixel-block" x="14" y="6" width="4" height="4" rx=".5" />
+              <rect class="pixel-block" x="6" y="14" width="4" height="4" rx=".5" />
+              <rect class="pixel-block" x="14" y="14" width="4" height="4" rx=".5" />
+            </svg>
+          </button>
+        </div>
+        <template v-if="mosaicMode === 'brush'">
+          <div class="settings-divider" />
+          <span class="setting-label">粗细</span>
+          <div class="setting-group stroke-group">
+            <button
+              v-for="widthValue in MOSAIC_WIDTHS"
+              :key="widthValue"
+              class="stroke-choice"
+              :class="{ active: mosaicBrushWidth === widthValue }"
+              :title="`${widthValue}px`"
+              @click="chooseMosaicWidth(widthValue)"
+            ><span :style="{ width: Math.min(22, widthValue / 2) + 'px', height: Math.min(22, widthValue / 2) + 'px' }" /></button>
+          </div>
+        </template>
+      </template>
+      <div v-else-if="activeTool !== 'text'" class="setting-group stroke-group">
         <button
           v-for="widthValue in STROKE_WIDTHS"
           :key="widthValue"
@@ -971,8 +1078,8 @@ onUnmounted(() => {
           {{ size }}
         </button>
       </div>
-      <div class="settings-divider" />
-      <div class="setting-group color-group">
+      <div v-if="!activeTool.startsWith('mosaic-')" class="settings-divider" />
+      <div v-if="!activeTool.startsWith('mosaic-')" class="setting-group color-group">
         <button
           v-for="color in colors"
           :key="color"
@@ -1171,7 +1278,7 @@ onUnmounted(() => {
 }
 
 .mark-toolbar {
-  width: 178px;
+  width: 212px;
 }
 .action-toolbar {
   box-sizing: border-box;
@@ -1183,7 +1290,8 @@ onUnmounted(() => {
 .action-btn,
 .swatch,
 .stroke-choice,
-.font-choice {
+.font-choice,
+.mode-choice {
   font-family: inherit;
 }
 
@@ -1341,6 +1449,53 @@ onUnmounted(() => {
   background: transparent;
   cursor: pointer;
 }
+.mosaic-mode-group {
+  gap: 0;
+  padding: 2px;
+  border-radius: 7px;
+  background: #e5e7eb;
+}
+.mode-choice {
+  display: grid;
+  place-items: center;
+  width: 36px;
+  min-width: 36px;
+  height: 30px;
+  padding: 0;
+  border: 0;
+  border-radius: 5px;
+  color: #475569;
+  background: transparent;
+  font-size: 13px;
+  font-weight: 600;
+  cursor: pointer;
+}
+.mode-choice svg {
+  width: 19px;
+  height: 19px;
+  fill: none;
+  stroke: currentColor;
+  stroke-width: 1.8;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+}
+.mode-choice svg .pixel-block {
+  fill: currentColor;
+  stroke: none;
+}
+.mode-choice:hover,
+.mode-choice.active {
+  color: #1d4ed8;
+  background: #fff;
+  box-shadow: 0 1px 3px rgba(15, 23, 42, 0.14);
+}
+.setting-label {
+  position: relative;
+  z-index: 1;
+  color: #64748b;
+  font-size: 12px;
+  white-space: nowrap;
+}
 .stroke-choice:hover,
 .stroke-choice.active,
 .font-choice:hover,
diff --git a/internal/application/annotation.go b/internal/application/annotation.go
index 80790fe..8563d15 100644
--- a/internal/application/annotation.go
+++ b/internal/application/annotation.go
@@ -81,6 +81,10 @@ func ApplyAnnotationsWithScale(pngBytes []byte, annotations []Annotation, scaleX
 			drawEllipseOutline(dst, ann.Points, scaleX, scaleY, width, c)
 		case "text":
 			drawTextAnnotation(dst, ann, scaleX, scaleY, c)
+		case "mosaic-brush":
+			applyMosaicBrush(dst, ann.Points, scaleX, scaleY, width)
+		case "mosaic-rect":
+			applyMosaicRect(dst, ann.Points, scaleX, scaleY)
 		}
 	}
 
@@ -91,6 +95,93 @@ func ApplyAnnotationsWithScale(pngBytes []byte, annotations []Annotation, scaleX
 	return buf.Bytes(), nil
 }
 
+const mosaicBlockSize = 10
+
+func applyMosaicBrush(img *image.RGBA, points []Point, scaleX, scaleY float64, width int) {
+	if len(points) == 0 {
+		return
+	}
+	mask := image.NewAlpha(img.Bounds())
+	maskColor := color.RGBA{A: 255}
+	if len(points) == 1 {
+		drawDotMask(mask, scalePoint(points[0], scaleX, scaleY), width, maskColor)
+	} else {
+		for i := 1; i < len(points); i++ {
+			drawMaskLine(mask, scalePoint(points[i-1], scaleX, scaleY), scalePoint(points[i], scaleX, scaleY), width, maskColor)
+		}
+	}
+	applyPixelation(img, img.Bounds(), mask)
+}
+
+func applyMosaicRect(img *image.RGBA, points []Point, scaleX, scaleY float64) {
+	if len(points) < 2 {
+		return
+	}
+	a := scalePoint(points[0], scaleX, scaleY)
+	b := scalePoint(points[len(points)-1], scaleX, scaleY)
+	x1, x2 := ordered(a.X, b.X)
+	y1, y2 := ordered(a.Y, b.Y)
+	r := image.Rect(int(math.Floor(x1)), int(math.Floor(y1)), int(math.Ceil(x2)), int(math.Ceil(y2))).Intersect(img.Bounds())
+	applyPixelation(img, r, nil)
+}
+
+func applyPixelation(img *image.RGBA, region image.Rectangle, mask *image.Alpha) {
+	if region.Empty() {
+		return
+	}
+	for y := region.Min.Y; y < region.Max.Y; y += mosaicBlockSize {
+		for x := region.Min.X; x < region.Max.X; x += mosaicBlockSize {
+			block := image.Rect(x, y, min(x+mosaicBlockSize, region.Max.X), min(y+mosaicBlockSize, region.Max.Y))
+			var r, g, b, a, count uint64
+			for py := block.Min.Y; py < block.Max.Y; py++ {
+				for px := block.Min.X; px < block.Max.X; px++ {
+					c := img.RGBAAt(px, py)
+					r += uint64(c.R)
+					g += uint64(c.G)
+					b += uint64(c.B)
+					a += uint64(c.A)
+					count++
+				}
+			}
+			if count == 0 {
+				continue
+			}
+			avg := color.RGBA{uint8(r / count), uint8(g / count), uint8(b / count), uint8(a / count)}
+			for py := block.Min.Y; py < block.Max.Y; py++ {
+				for px := block.Min.X; px < block.Max.X; px++ {
+					if mask == nil || mask.AlphaAt(px, py).A > 0 {
+						img.SetRGBA(px, py, avg)
+					}
+				}
+			}
+		}
+	}
+}
+
+func drawMaskLine(mask *image.Alpha, a, b Point, width int, c color.RGBA) {
+	dx, dy := b.X-a.X, b.Y-a.Y
+	steps := int(math.Max(math.Abs(dx), math.Abs(dy)))
+	if steps == 0 {
+		drawDotMask(mask, a, width, c)
+		return
+	}
+	for i := 0; i <= steps; i++ {
+		t := float64(i) / float64(steps)
+		drawDotMask(mask, Point{X: a.X + dx*t, Y: a.Y + dy*t}, width, c)
+	}
+}
+
+func drawDotMask(mask *image.Alpha, p Point, width int, c color.RGBA) {
+	radius := float64(width) / 2
+	for y := int(math.Floor(p.Y - radius)); y <= int(math.Ceil(p.Y+radius)); y++ {
+		for x := int(math.Floor(p.X - radius)); x <= int(math.Ceil(p.X+radius)); x++ {
+			if image.Pt(x, y).In(mask.Bounds()) && math.Hypot(float64(x)-p.X, float64(y)-p.Y) <= radius {
+				mask.SetAlpha(x, y, color.Alpha{A: c.A})
+			}
+		}
+	}
+}
+
 func parseHexColor(hex string) (color.RGBA, error) {
 	value := strings.TrimPrefix(strings.TrimSpace(hex), "#")
 	if len(value) != 6 {
diff --git a/internal/application/annotation_test.go b/internal/application/annotation_test.go
index 2962429..7407bd4 100644
--- a/internal/application/annotation_test.go
+++ b/internal/application/annotation_test.go
@@ -171,3 +171,61 @@ func TestApplyAnnotationsUsesStrokeWidth(t *testing.T) {
 		t.Fatalf("expected thick rectangle stroke to cover y=24, got %#v", got)
 	}
 }
+
+func TestApplyAnnotationsPixelatesMosaicRectangle(t *testing.T) {
+	src := image.NewRGBA(image.Rect(0, 0, 40, 30))
+	for y := 0; y < 30; y++ {
+		for x := 0; x < 40; x++ {
+			src.SetRGBA(x, y, color.RGBA{R: uint8(x * 6), G: uint8(y * 8), B: uint8((x + y) * 3), A: 255})
+		}
+	}
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, src); err != nil {
+		t.Fatalf("encode source: %v", err)
+	}
+	out, err := ApplyAnnotations(buf.Bytes(), []Annotation{{
+		Tool: "mosaic-rect", Points: []Point{{X: 10, Y: 5}, {X: 30, Y: 25}},
+	}}, 1)
+	if err != nil {
+		t.Fatalf("apply annotations: %v", err)
+	}
+	img, err := png.Decode(bytes.NewReader(out))
+	if err != nil {
+		t.Fatalf("decode output: %v", err)
+	}
+	if img.At(12, 7) != img.At(18, 13) {
+		t.Fatalf("expected pixels in one mosaic block to share a color")
+	}
+	if img.At(5, 5) != src.At(5, 5) {
+		t.Fatalf("expected pixels outside mosaic rectangle to remain unchanged")
+	}
+}
+
+func TestApplyAnnotationsPixelatesOnlyMosaicBrushStroke(t *testing.T) {
+	src := image.NewRGBA(image.Rect(0, 0, 50, 30))
+	for y := 0; y < 30; y++ {
+		for x := 0; x < 50; x++ {
+			src.SetRGBA(x, y, color.RGBA{R: uint8(x * 5), G: uint8(y * 8), A: 255})
+		}
+	}
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, src); err != nil {
+		t.Fatalf("encode source: %v", err)
+	}
+	out, err := ApplyAnnotations(buf.Bytes(), []Annotation{{
+		Tool: "mosaic-brush", StrokeWidth: 12, Points: []Point{{X: 5, Y: 15}, {X: 45, Y: 15}},
+	}}, 1)
+	if err != nil {
+		t.Fatalf("apply annotations: %v", err)
+	}
+	img, err := png.Decode(bytes.NewReader(out))
+	if err != nil {
+		t.Fatalf("decode output: %v", err)
+	}
+	if img.At(12, 15) == src.At(12, 15) {
+		t.Fatalf("expected brush path to be pixelated")
+	}
+	if img.At(12, 2) != src.At(12, 2) {
+		t.Fatalf("expected pixels outside brush path to remain unchanged")
+	}
+}
diff --git a/native_overlay_darwin.go b/native_overlay_darwin.go
index 8aaf032..a490d04 100644
--- a/native_overlay_darwin.go
+++ b/native_overlay_darwin.go
@@ -142,8 +142,14 @@ static id nativeOverlayKeyMonitor = nil;
 @property(strong) NSColor *activeColor;
 @property CGFloat activeStrokeWidth;
 @property CGFloat activeFontSize;
+@property CGFloat mosaicBrushWidth;
+@property NSString *mosaicMode;
 @property(strong) NSMutableArray<NSDictionary *> *annotations;
 @property(strong) NSMutableDictionary *draftAnnotation;
+// A downsampled snapshot of the screen beneath the overlay. Drawing this
+// image back at full size with interpolation disabled produces a genuine
+// pixel-block preview instead of a translucent placeholder stroke.
+@property(strong) NSImage *mosaicPreviewImage;
 @property(strong) NSButton *cancelButton;
 // Use `clipboardButton` (not `copyButton`) to avoid ARC's "copy" method
 // family ownership rule which would otherwise treat the synthesized getter
@@ -159,12 +165,15 @@ static id nativeOverlayKeyMonitor = nil;
 @property(strong) NSButton *rectButton;
 @property(strong) NSButton *ellipseButton;
 @property(strong) NSButton *textButton;
+@property(strong) NSButton *mosaicButton;
 @property(strong) NSButton *undoButton;
 @property(strong) SnipToolSettingsView *toolSettingsView;
 @property(strong) NSView *settingsDivider;
 @property(strong) NSMutableArray<NSButton *> *strokeSettingButtons;
 @property(strong) NSMutableArray<NSButton *> *fontSettingButtons;
 @property(strong) NSMutableArray<NSButton *> *colorSettingButtons;
+@property(strong) NSMutableArray<NSButton *> *mosaicModeButtons;
+@property(strong) NSMutableArray<NSButton *> *mosaicWidthButtons;
 @property(strong) NSView *actionToolbarBg;
 @property(strong) NSTextField *textEditor;
 @property NSPoint textEditorLocalPoint;
@@ -195,6 +204,8 @@ static id nativeOverlayKeyMonitor = nil;
 - (void)selectStrokeWidth:(NSButton *)sender;
 - (void)selectFontSize:(NSButton *)sender;
 - (void)selectToolColor:(NSButton *)sender;
+- (void)selectMosaicMode:(NSButton *)sender;
+- (void)selectMosaicWidth:(NSButton *)sender;
 - (BOOL)isEditingText;
 - (void)commitTextEditor;
 - (void)cancelTextEditor;
@@ -214,6 +225,8 @@ static id nativeOverlayKeyMonitor = nil;
         _activeColor = [NSColor colorWithCalibratedRed:239.0/255.0 green:68.0/255.0 blue:68.0/255.0 alpha:1.0];
         _activeStrokeWidth = 3.0;
         _activeFontSize = 20.0;
+        _mosaicBrushWidth = 24.0;
+        _mosaicMode = @"brush";
         _annotations = [NSMutableArray array];
         _textEditorAnnotationIndex = -1;
         _selectedTextAnnotationIndex = -1;
@@ -243,12 +256,15 @@ static id nativeOverlayKeyMonitor = nil;
         _rectButton = [NSButton buttonWithTitle:@"" target:self action:@selector(selectRect)];
         _ellipseButton = [NSButton buttonWithTitle:@"" target:self action:@selector(selectEllipse)];
         _textButton = [NSButton buttonWithTitle:@"" target:self action:@selector(selectText)];
+        _mosaicButton = [NSButton buttonWithTitle:@"" target:self action:@selector(selectMosaic)];
         _undoButton = [NSButton buttonWithTitle:@"" target:self action:@selector(undoAnnotation)];
         _toolSettingsView = [[SnipToolSettingsView alloc] initWithFrame:NSZeroRect];
         _settingsDivider = [[NSView alloc] initWithFrame:NSZeroRect];
         _strokeSettingButtons = [NSMutableArray array];
         _fontSettingButtons = [NSMutableArray array];
         _colorSettingButtons = [NSMutableArray array];
+        _mosaicModeButtons = [NSMutableArray array];
+        _mosaicWidthButtons = [NSMutableArray array];
         // Dark rounded background container behind the action icon buttons,
         // mirroring the look of `.action-toolbar` in the Vue overlay.
         _actionToolbarBg = [[NSView alloc] initWithFrame:NSZeroRect];
@@ -262,10 +278,10 @@ static id nativeOverlayKeyMonitor = nil;
         // Add the action toolbar background BEFORE the buttons so it sits
         // behind them in the view hierarchy (AppKit z-order = subview order).
         [self addSubview:_actionToolbarBg];
-        for (NSView *view in @[_cancelButton, _clipboardButton, _saveButton, _saveRemoteButton, _ftpButton, _ocrButton, _summaryButton, _uploadButton, _penButton, _rectButton, _ellipseButton, _textButton, _undoButton, _toolSettingsView, _sizeLabel, _hintLabel]) {
+        for (NSView *view in @[_cancelButton, _clipboardButton, _saveButton, _saveRemoteButton, _ftpButton, _ocrButton, _summaryButton, _uploadButton, _penButton, _rectButton, _ellipseButton, _textButton, _mosaicButton, _undoButton, _toolSettingsView, _sizeLabel, _hintLabel]) {
             [self addSubview:view];
         }
-        for (NSView *view in @[_cancelButton, _clipboardButton, _saveButton, _saveRemoteButton, _ftpButton, _ocrButton, _summaryButton, _uploadButton, _penButton, _rectButton, _ellipseButton, _textButton, _undoButton, _toolSettingsView, _actionToolbarBg]) {
+        for (NSView *view in @[_cancelButton, _clipboardButton, _saveButton, _saveRemoteButton, _ftpButton, _ocrButton, _summaryButton, _uploadButton, _penButton, _rectButton, _ellipseButton, _textButton, _mosaicButton, _undoButton, _toolSettingsView, _actionToolbarBg]) {
             [view setHidden:YES];
         }
         [_sizeLabel setHidden:YES];
@@ -381,6 +397,8 @@ static id nativeOverlayKeyMonitor = nil;
     [self styleIconButton:_rectButton image:[self iconFromSVG:@"<svg viewBox='0 0 1024 1024' xmlns='http://www.w3.org/2000/svg'><path d='M96 96h832v832H96V96z m32 32v768h768V128H128z' fill='white'/></svg>"]];
     [self styleIconButton:_ellipseButton image:[self iconFromSVG:@"<svg viewBox='0 0 1024 1024' xmlns='http://www.w3.org/2000/svg'><path d='M512 928c229.76 0 416-186.24 416-416S741.76 96 512 96 96 282.24 96 512s186.24 416 416 416z m0-32C299.936 896 128 724.064 128 512S299.936 128 512 128s384 171.936 384 384-171.936 384-384 384z' fill='white'/></svg>"]];
     [self styleIconButton:_textButton image:[self iconFromSVG:@"<svg viewBox='0 0 1024 1024' xmlns='http://www.w3.org/2000/svg'><path d='M224 160h576v96H560v608h-96V256H224V160zM384 864h256v64H384v-64z' fill='white'/></svg>"]];
+    [self styleIconButton:_mosaicButton image:[self iconFromSVG:@"<svg viewBox='0 0 1024 1024' xmlns='http://www.w3.org/2000/svg'><path d='M128 128h320v320H128V128zm448 0h320v320H576V128zM128 576h320v320H128V576zm448 0h320v320H576V576z' fill='white'/></svg>"]];
+    [_mosaicButton setToolTip:@"马赛克标记"];
     [self styleIconButton:_undoButton image:[self iconFromSVG:@"<svg viewBox='0 0 1024 1024' xmlns='http://www.w3.org/2000/svg'><g transform='translate(1024 0) scale(-1 1)'><path d='M838.976 288l-169.344-162.56a16 16 0 1 1 22.144-23.04l213.632 204.992-213.312 215.84a16 16 0 0 1-22.784-22.464L847.936 320H454.56c-164.192 0-297.28 128.96-297.28 288s133.088 288 297.28 288H704v32h-242.784C266.88 928 128 784.736 128 608S266.88 288 461.248 288h377.728z' fill='white'/></g></svg>"]];
 
     [_toolSettingsView setWantsLayer:NO];
@@ -415,6 +433,37 @@ static id nativeOverlayKeyMonitor = nil;
         [_toolSettingsView addSubview:button];
     }
 
+    for (NSUInteger i = 0; i < 2; i++) {
+        NSButton *button = [NSButton buttonWithTitle:@"" target:self action:@selector(selectMosaicMode:)];
+        [button setTag:(NSInteger)i];
+        [button setBordered:NO];
+        [button setWantsLayer:YES];
+        [[button layer] setCornerRadius:5];
+        NSString *svg = i == 0
+            ? @"<svg viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'><g fill='none' stroke='black' stroke-width='1.8' stroke-linecap='round' stroke-linejoin='round'><path d='M9 11V5.5a2 2 0 0 1 4 0V10'/><path d='M13 10V8a2 2 0 0 1 4 0v3'/><path d='M17 10a2 2 0 0 1 4 0v4.5c0 4-2.5 6.5-6.5 6.5h-1.2a6 6 0 0 1-4.7-2.3L4 13.2a1.9 1.9 0 0 1 2.8-2.5L9 12.5'/></g></svg>"
+            : @"<svg viewBox='0 0 24 24' xmlns='http://www.w3.org/2000/svg'><g fill='none' stroke='black' stroke-width='1.8' stroke-linejoin='round'><rect x='2.5' y='2.5' width='19' height='19' rx='2'/></g><g fill='black'><rect x='6' y='6' width='4' height='4' rx='.5'/><rect x='14' y='6' width='4' height='4' rx='.5'/><rect x='6' y='14' width='4' height='4' rx='.5'/><rect x='14' y='14' width='4' height='4' rx='.5'/></g></svg>";
+        [button setImage:[self iconFromSVG:svg]];
+        [button setImagePosition:NSImageOnly];
+        [button setImageScaling:NSImageScaleProportionallyDown];
+        NSString *accessibilityLabel = i == 0 ? @"涂抹马赛克" : @"框选马赛克";
+        [button setToolTip:accessibilityLabel];
+        [button setAccessibilityLabel:accessibilityLabel];
+        [_mosaicModeButtons addObject:button];
+        [_toolSettingsView addSubview:button];
+    }
+    for (NSNumber *width in @[@16, @24, @36, @52]) {
+        NSButton *button = [NSButton buttonWithTitle:@"●" target:self action:@selector(selectMosaicWidth:)];
+        [button setTag:[width integerValue]];
+        [button setBordered:NO];
+        [button setWantsLayer:YES];
+        [[button layer] setCornerRadius:6];
+        NSMutableAttributedString *title = [[NSMutableAttributedString alloc] initWithString:@"●"];
+        [title addAttribute:NSFontAttributeName value:[NSFont systemFontOfSize:MIN(22, 6 + [width doubleValue] / 3) weight:NSFontWeightBold] range:NSMakeRange(0, title.length)];
+        [button setAttributedTitle:title];
+        [_mosaicWidthButtons addObject:button];
+        [_toolSettingsView addSubview:button];
+    }
+
     NSArray *colors = @[
         [NSColor colorWithCalibratedRed:239.0/255.0 green:68.0/255.0 blue:68.0/255.0 alpha:1.0],
         [NSColor colorWithCalibratedRed:250.0/255.0 green:204.0/255.0 blue:21.0/255.0 alpha:1.0],
@@ -629,6 +678,63 @@ static id nativeOverlayKeyMonitor = nil;
             }
             continue;
         }
+        if ([tool hasPrefix:@"mosaic-"]) {
+            [NSGraphicsContext saveGraphicsState];
+            NSBezierPath *clipPath = nil;
+            if ([tool isEqualToString:@"mosaic-brush"]) {
+                clipPath = [NSBezierPath bezierPath];
+                CGFloat radius = [self strokeWidthForItem:item] / 2.0;
+                for (NSUInteger i = 0; i < points.count; i++) {
+                    NSPoint local = [points[i] pointValue];
+                    NSPoint p = NSMakePoint(_selection.origin.x + local.x, _selection.origin.y + local.y);
+                    [clipPath appendBezierPathWithOvalInRect:NSMakeRect(p.x - radius, p.y - radius, radius * 2, radius * 2)];
+                    if (i == 0) continue;
+                    NSPoint previousLocal = [points[i - 1] pointValue];
+                    NSPoint previous = NSMakePoint(_selection.origin.x + previousLocal.x, _selection.origin.y + previousLocal.y);
+                    CGFloat dx = p.x - previous.x, dy = p.y - previous.y;
+                    CGFloat length = hypot(dx, dy);
+                    if (length <= 0.001) continue;
+                    CGFloat nx = -dy / length * radius, ny = dx / length * radius;
+                    NSBezierPath *segment = [NSBezierPath bezierPath];
+                    [segment moveToPoint:NSMakePoint(previous.x + nx, previous.y + ny)];
+                    [segment lineToPoint:NSMakePoint(p.x + nx, p.y + ny)];
+                    [segment lineToPoint:NSMakePoint(p.x - nx, p.y - ny)];
+                    [segment lineToPoint:NSMakePoint(previous.x - nx, previous.y - ny)];
+                    [segment closePath];
+                    [clipPath appendBezierPath:segment];
+                }
+            } else if (points.count >= 2) {
+                NSPoint a = [points[0] pointValue], b = [[points lastObject] pointValue];
+                NSRect r = NSMakeRect(_selection.origin.x + MIN(a.x, b.x), _selection.origin.y + MIN(a.y, b.y), fabs(b.x-a.x), fabs(b.y-a.y));
+                clipPath = [NSBezierPath bezierPathWithRect:r];
+            }
+            if (clipPath != nil) {
+                [clipPath addClip];
+                if (_mosaicPreviewImage != nil) {
+                    NSDictionary *hints = @{NSImageHintInterpolation: @(NSImageInterpolationNone)};
+                    [_mosaicPreviewImage drawInRect:self.bounds
+                                          fromRect:NSMakeRect(0, 0, _mosaicPreviewImage.size.width, _mosaicPreviewImage.size.height)
+                                         operation:NSCompositingOperationCopy
+                                          fraction:1.0
+                                    respectFlipped:YES
+                                             hints:hints];
+                } else {
+                    // Screen capture can be unavailable before Screen Recording
+                    // permission is granted. A checkerboard fallback still reads
+                    // as pixelation and never resembles a marker stroke.
+                    CGFloat tile = 8.0;
+                    for (CGFloat y = 0; y < self.bounds.size.height; y += tile) {
+                        for (CGFloat x = 0; x < self.bounds.size.width; x += tile) {
+                            BOOL alternate = (((NSInteger)(x / tile) + (NSInteger)(y / tile)) % 2) == 0;
+                            [[NSColor colorWithCalibratedWhite:(alternate ? 0.42 : 0.68) alpha:1.0] setFill];
+                            NSRectFill(NSMakeRect(x, y, tile, tile));
+                        }
+                    }
+                }
+            }
+            [NSGraphicsContext restoreGraphicsState];
+            continue;
+        }
         [color setStroke];
         CGFloat strokeWidth = [self strokeWidthForItem:item];
         NSBezierPath *path = [NSBezierPath bezierPath];
@@ -805,7 +911,7 @@ static id nativeOverlayKeyMonitor = nil;
             @"tool": _activeTool,
             @"color": [self hexForColor:_activeColor],
             @"nsColor": _activeColor,
-            @"strokeWidth": @(_activeStrokeWidth),
+            @"strokeWidth": @([_activeTool isEqualToString:@"mosaic-brush"] ? _mosaicBrushWidth : _activeStrokeWidth),
             @"points": [NSMutableArray arrayWithObject:[NSValue valueWithPoint:local]]
         } mutableCopy];
     } else if (_hasSelection && NSPointInRect(p, _selection)) {
@@ -869,7 +975,7 @@ static id nativeOverlayKeyMonitor = nil;
     } else if (_annotating && _draftAnnotation != nil) {
         NSMutableArray *points = _draftAnnotation[@"points"];
         NSPoint local = [self localPoint:p];
-        if ([_activeTool isEqualToString:@"pen"]) {
+        if ([_activeTool isEqualToString:@"pen"] || [_activeTool isEqualToString:@"mosaic-brush"]) {
             [points addObject:[NSValue valueWithPoint:local]];
         } else {
             if (points.count == 1) {
@@ -939,6 +1045,7 @@ static id nativeOverlayKeyMonitor = nil;
     [_rectButton setHidden:!visible];
     [_ellipseButton setHidden:!visible];
     [_textButton setHidden:!visible];
+    [_mosaicButton setHidden:!visible];
     [_undoButton setHidden:!visible];
     [_toolSettingsView setHidden:!visible || _activeTool == nil];
     [_sizeLabel setHidden:!visible];
@@ -981,20 +1088,23 @@ static id nativeOverlayKeyMonitor = nil;
 
     // Mark toolbar sits to the LEFT of the action toolbar (same row) with an
     // 8px gap between the two groups, so they never overlap on tiny selections.
-    CGFloat markW = 178;
+    CGFloat markW = 212;
     CGFloat markGap = 8;
     CGFloat markX = MAX(0, x - markGap - markW);
     [_penButton setFrame:NSMakeRect(markX + 4, y + 4, 28, 28)];
     [_rectButton setFrame:NSMakeRect(markX + 38, y + 4, 28, 28)];
     [_ellipseButton setFrame:NSMakeRect(markX + 72, y + 4, 28, 28)];
     [_textButton setFrame:NSMakeRect(markX + 106, y + 4, 28, 28)];
-    [_undoButton setFrame:NSMakeRect(markX + 144, y + 4, 28, 28)];
+    [_mosaicButton setFrame:NSMakeRect(markX + 140, y + 4, 28, 28)];
+    [_undoButton setFrame:NSMakeRect(markX + 178, y + 4, 28, 28)];
     [_undoButton setEnabled:YES];
     [[_undoButton layer] setOpacity:_annotations.count > 0 ? 1.0 : 0.35];
 
     if (_activeTool != nil) {
         BOOL isText = [_activeTool isEqualToString:@"text"];
-        CGFloat settingsW = isText ? 462 : 398;
+        BOOL isMosaic = [_activeTool hasPrefix:@"mosaic-"];
+        BOOL mosaicBrush = [_mosaicMode isEqualToString:@"brush"];
+        CGFloat settingsW = isMosaic ? (mosaicBrush ? 304 : 112) : (isText ? 462 : 398);
         CGFloat settingsH = 58;
         CGFloat settingsX = MAX(8, MIN(markX, self.bounds.size.width - settingsW - 8));
         CGFloat settingsY = y + toolbarH + 4;
@@ -1005,6 +1115,7 @@ static id nativeOverlayKeyMonitor = nil;
         if ([_activeTool isEqualToString:@"rect"]) activeCenter = markX + 52;
         if ([_activeTool isEqualToString:@"ellipse"]) activeCenter = markX + 86;
         if ([_activeTool isEqualToString:@"text"]) activeCenter = markX + 120;
+        if (isMosaic) activeCenter = markX + 154;
         [_toolSettingsView setFrame:NSMakeRect(settingsX, settingsY, settingsW, settingsH)];
         [_toolSettingsView setArrowX:MAX(18, MIN(activeCenter - settingsX, settingsW - 18))];
         [_toolSettingsView setNeedsDisplay:YES];
@@ -1012,21 +1123,34 @@ static id nativeOverlayKeyMonitor = nil;
         CGFloat contentY = 18;
         CGFloat xCursor = 14;
         for (NSButton *button in _strokeSettingButtons) {
-            [button setHidden:isText];
+            [button setHidden:isText || isMosaic];
             [button setFrame:NSMakeRect(xCursor, contentY, 32, 32)];
             xCursor += 42;
         }
         xCursor = 14;
         for (NSButton *button in _fontSettingButtons) {
-            [button setHidden:!isText];
+            [button setHidden:!isText || isMosaic];
             [button setFrame:NSMakeRect(xCursor, contentY, 40, 32)];
             xCursor += 48;
         }
+        for (NSUInteger i = 0; i < _mosaicModeButtons.count; i++) {
+            NSButton *button = _mosaicModeButtons[i];
+            [button setHidden:!isMosaic];
+            [button setFrame:NSMakeRect(14 + i * 38, contentY + 1, 36, 30)];
+        }
+        for (NSUInteger i = 0; i < _mosaicWidthButtons.count; i++) {
+            NSButton *button = _mosaicWidthButtons[i];
+            [button setHidden:!isMosaic || !mosaicBrush];
+            [button setFrame:NSMakeRect(122 + i * 42, contentY, 32, 32)];
+        }
         CGFloat groupW = isText ? (4 * 40 + 3 * 8) : (3 * 32 + 2 * 10);
         CGFloat dividerX = 14 + groupW + 12;
+        [_settingsDivider setHidden:isMosaic && !mosaicBrush];
+        if (isMosaic) dividerX = 102;
         [_settingsDivider setFrame:NSMakeRect(dividerX, contentY + 3, 1, 26)];
         CGFloat colorX = dividerX + 18;
         for (NSButton *button in _colorSettingButtons) {
+            [button setHidden:isMosaic];
             [button setFrame:NSMakeRect(colorX, contentY + 5, 22, 22)];
             colorX += 34;
         }
@@ -1043,6 +1167,8 @@ static id nativeOverlayKeyMonitor = nil;
             : [NSColor clearColor];
         [[button layer] setBackgroundColor:[bg CGColor]];
     }
+    BOOL mosaicActive = [_activeTool hasPrefix:@"mosaic-"];
+    [[_mosaicButton layer] setBackgroundColor:[(mosaicActive ? [NSColor colorWithCalibratedWhite:1.0 alpha:0.14] : [NSColor clearColor]) CGColor]];
     [self updateToolSettingsStates];
 }
 
@@ -1070,6 +1196,23 @@ static id nativeOverlayKeyMonitor = nil;
             [button setAttributedTitle:title];
         }
     }
+    for (NSButton *button in _mosaicModeButtons) {
+        BOOL active = (button.tag == 0 && [_mosaicMode isEqualToString:@"brush"]) || (button.tag == 1 && [_mosaicMode isEqualToString:@"rect"]);
+        [self styleButton:button background:(active ? [NSColor whiteColor] : clear) foreground:(active ? activeFg : normalFg)];
+        if (@available(macOS 10.14, *)) {
+            [button setContentTintColor:(active ? activeFg : normalFg)];
+        }
+        [button setAccessibilityValue:(active ? @"已选择" : @"未选择")];
+    }
+    for (NSButton *button in _mosaicWidthButtons) {
+        BOOL active = fabs((CGFloat)button.tag - _mosaicBrushWidth) < 0.1;
+        [[button layer] setBackgroundColor:[(active ? activeBg : clear) CGColor]];
+        NSMutableAttributedString *title = [[button attributedTitle] mutableCopy];
+        if (title.length > 0) {
+            [title addAttribute:NSForegroundColorAttributeName value:(active ? activeFg : normalFg) range:NSMakeRange(0, title.length)];
+            [button setAttributedTitle:title];
+        }
+    }
 
     NSString *activeHex = [self hexForColor:_activeColor];
     NSArray *colors = objc_getAssociatedObject(_toolSettingsView, "snapgoColors");
@@ -1090,6 +1233,7 @@ static id nativeOverlayKeyMonitor = nil;
 - (void)selectRect { [self selectTool:@"rect"]; }
 - (void)selectEllipse { [self selectTool:@"ellipse"]; }
 - (void)selectText { [self selectTool:@"text"]; }
+- (void)selectMosaic { [self selectTool:[_mosaicMode isEqualToString:@"brush"] ? @"mosaic-brush" : @"mosaic-rect"]; }
 - (void)undoAnnotation {
     if (_annotations.count == 0 && _textEditor == nil) {
         return;
@@ -1228,6 +1372,16 @@ static id nativeOverlayKeyMonitor = nil;
     [self updateToolSettingsStates];
 }
 
+- (void)selectMosaicMode:(NSButton *)sender {
+    _mosaicMode = sender.tag == 0 ? @"brush" : @"rect";
+    [self selectMosaic];
+}
+
+- (void)selectMosaicWidth:(NSButton *)sender {
+    _mosaicBrushWidth = MAX(8.0, (CGFloat)sender.tag);
+    [self updateToolSettingsStates];
+}
+
 - (void)selectFontSize:(NSButton *)sender {
     _activeFontSize = MAX(8.0, (CGFloat)sender.tag);
     if (_textEditor != nil) {
@@ -1421,6 +1575,60 @@ static NSScreen *snipScreenContainingCursor(void) {
     return [[NSScreen screens] firstObject];
 }
 
+// snipMosaicPreviewImage captures the target display before the transparent
+// overlay becomes visible, then downsamples it to one sample per 10 logical
+// points. The view scales this tiny image back with nearest-neighbour
+// interpolation inside each mosaic mask, yielding stable, screen-derived
+// pixel blocks while the pointer is moving.
+static NSImage *snipMosaicPreviewImage(NSScreen *screen) {
+    NSSize fullSize = [screen frame].size;
+    NSUInteger screenIndex = [[NSScreen screens] indexOfObjectIdenticalTo:screen];
+    if (screenIndex == NSNotFound) screenIndex = 0;
+    NSString *temporaryPath = [NSTemporaryDirectory() stringByAppendingPathComponent:
+        [NSString stringWithFormat:@"snapgo-mosaic-%@.png", [[NSUUID UUID] UUIDString]]];
+    NSTask *captureTask = [[NSTask alloc] init];
+    [captureTask setExecutableURL:[NSURL fileURLWithPath:@"/usr/sbin/screencapture"]];
+    [captureTask setArguments:@[@"-x", @"-D", [NSString stringWithFormat:@"%lu", (unsigned long)screenIndex + 1], temporaryPath]];
+    NSError *launchError = nil;
+    if (![captureTask launchAndReturnError:&launchError]) return nil;
+    [captureTask waitUntilExit];
+    NSImage *fullImage = [[NSImage alloc] initWithContentsOfFile:temporaryPath];
+    [[NSFileManager defaultManager] removeItemAtPath:temporaryPath error:nil];
+    if ([captureTask terminationStatus] != 0 || fullImage == nil) return nil;
+
+    NSInteger pixelW = MAX(1, (NSInteger)ceil(fullSize.width / 10.0));
+    NSInteger pixelH = MAX(1, (NSInteger)ceil(fullSize.height / 10.0));
+    NSBitmapImageRep *bitmap = [[NSBitmapImageRep alloc]
+        initWithBitmapDataPlanes:NULL
+                      pixelsWide:pixelW
+                      pixelsHigh:pixelH
+                   bitsPerSample:8
+                 samplesPerPixel:4
+                        hasAlpha:YES
+                        isPlanar:NO
+                  colorSpaceName:NSCalibratedRGBColorSpace
+                     bytesPerRow:0
+                    bitsPerPixel:0];
+    if (bitmap == nil) return nil;
+
+    NSGraphicsContext *context = [NSGraphicsContext graphicsContextWithBitmapImageRep:bitmap];
+    [NSGraphicsContext saveGraphicsState];
+    [NSGraphicsContext setCurrentContext:context];
+    [context setImageInterpolation:NSImageInterpolationHigh];
+    [fullImage drawInRect:NSMakeRect(0, 0, pixelW, pixelH)
+                 fromRect:NSMakeRect(0, 0, fullSize.width, fullSize.height)
+                operation:NSCompositingOperationCopy
+                 fraction:1.0
+           respectFlipped:NO
+                    hints:nil];
+    [context flushGraphics];
+    [NSGraphicsContext restoreGraphicsState];
+
+    NSImage *result = [[NSImage alloc] initWithSize:NSMakeSize(pixelW, pixelH)];
+    [result addRepresentation:bitmap];
+    return result;
+}
+
 static void snipShowNativeOverlay(int width, int height) {
     dispatch_async(dispatch_get_main_queue(), ^{
         NSScreen *screen = snipScreenContainingCursor();
@@ -1430,6 +1638,7 @@ static void snipShowNativeOverlay(int width, int height) {
         }
 
         NSRect frame = [screen frame];
+        NSImage *mosaicPreview = snipMosaicPreviewImage(screen);
         [NSApp activateIgnoringOtherApps:YES];
 
         nativeOverlayWindow = [[SnipNativeOverlayPanel alloc]
@@ -1450,6 +1659,7 @@ static void snipShowNativeOverlay(int width, int height) {
 
         SnipNativeOverlayView *view = [[SnipNativeOverlayView alloc]
             initWithFrame:NSMakeRect(0, 0, frame.size.width, frame.size.height)];
+        [view setMosaicPreviewImage:mosaicPreview];
         [nativeOverlayWindow setContentView:view];
         [nativeOverlayWindow makeKeyAndOrderFront:nil];
         [nativeOverlayWindow makeFirstResponder:view];