How to Annotate Screenshots on Mac: Draw, Highlight & Crop with AldooSnap

Mark Up Your Screenshots with AldooSnap's Annotation Tools

AldooSnap lets you draw, highlight, label, measure, blur, and crop directly on a captured image before you save or share it. Most of these tools show up in two places: the selection bar while you're capturing an Area, and the preview window that opens after a Screen, Window, or Scroll Snap capture, or after tapping Annotate on a photo in the Photo Booth's film roll. Cropping is the one exception — it's only available in the preview window.

Drawing and Marking Tools

Five tools cover freehand marks and simple shapes, all drawn by clicking and dragging on the image.

1. Select Pen to draw a thin freehand line.
2. Select Highlighter to draw a wider, semi-transparent stroke for highlighting text or areas.
3. Select Line to drag a straight line between two points. Shift-drag to draw the line in ortho mode switching between 45 degrees.
4. Select Arrow to drag a straight arrow pointing at something in the image.
5. Select Rectangle to drag an outlined box around a region.

Numbered Steps and Text

Use these to label a screenshot for a tutorial or walkthrough.

1. Select Numbered step and click anywhere on the image to drop a numbered badge — each one you place counts up automatically (1, 2, 3…), and deleting one renumbers the rest.
2. Select Text and click to drop a text box, which opens for editing immediately.
3. Double-click an existing text box or numbered step to reposition or edit it, or drag it to move it.
4. Shift-click a text box or numbered step to delete it.

Rulers and Guides

Use these as visual alignment references while you place other annotations — guides never get baked into the saved image.

1. Click Rulers (or Show/hide rulers in the preview window) to reveal rulers along the top and left edges.
2. Click the top ruler to drop a vertical guide, or the left ruler to drop a horizontal guide.
3. Drag a guide to reposition it — dragging with Option held duplicates it instead of moving the original.
4. When two guides on the same axis sit near each other, a chip shows the pixel distance between them.
5. Click the ⊗ at a guide's end on the ruler to delete it.

Measuring Distances

Use this when you need to call out an exact pixel measurement, like a spacing or sizing detail.

1. Select Measure distance in pixels and drag between two points to drop a ruler line with its length labeled in pixels. Shift-drag to draw the measure line in ortho mode switching between 45 degrees.
2. Drag either endpoint afterward to adjust the measurement — the label updates as you drag.

Blurring Sensitive Content

Use this to redact things like emails, names, or account numbers before sharing a capture.

1. Select Blur an area (smooth or pixelated) and drag out a rectangle over the content you want to hide.
2. Use the floating panel that appears to pick a style — Smooth, Pixels, Solid, or Emoji — and adjust the strength slider.
3. With Emoji selected, click Open Emoji Picker… to choose which emoji covers the area, and drag its rotation knob to angle it.
4. Drag the rectangle's corner handles to resize it, or drag the rectangle itself to move it.
5. Click the blue ⊗ badge above the rectangle to remove a blur you no longer want.

Picking Colors

Three separate tools handle color, each for a different job: setting what you draw with, discovering colors already in the image, and grabbing an exact pixel's value.

1. Click the color swatch to set the active drawing color from a preset palette — this is the color every Pen, Highlighter, Line, Arrow, Rectangle, and Text annotation uses.
2. Click Extract color palette to generate a set of dominant colors pulled from the image itself, useful for finding colors already used in a design or screenshot.
3. Click the eyedropper, then click anywhere on the image to sample that exact pixel's color and copy its hex value to the clipboard — useful for matching a specific color rather than an approximate one.

Cropping an Image

Cropping is only available in the preview window — not in the inline Area-capture bar. That preview window opens automatically after a Screen or Window capture, after a Scroll Snap finishes stitching, or when you click Annotate on a photo in the Photo Booth's film roll.

1. Select Crop and drag out the region you want to keep.
2. Drag inside the pending crop rectangle to reposition it, or draw a new one to start over.
3. Click Apply Crop, press Enter, or double-click inside the rectangle to apply it.

Undo and Zoom

The preview window's toolbar also carries two housekeeping controls.

1. Click Undo last annotation to remove the most recent mark you made.
2. Click Zoom in or Zoom out to get a closer look while annotating a large or detailed capture.

Finishing Up

Once you're done marking up a capture, finish it the same way as any other image: Copy share link (which will add the capture to Your Files gallery in your account on AldooSnap website), Copy to clipboard, or Save — or Close to dismiss without saving. Every saved file lands in the same place; click the AldooSnap icon in the menu bar and choose Recordings to open that folder directly in Finder.