Image annotate

Image Annotate

Mark up an existing image with shapes, text, numbered steps, blur, or solid-color redaction. Single CLI, one-off flags for simple marks, JSON spec file for compositions. Output is a flat raster image with every mark burned in - the original is never modified in place.

Core Principles

Principle	Meaning
Never modify in place	Always write to a new output file. Annotation is destructive - the user must keep the original to redo or refine later.
Blur is not redaction	Pixelation and blur can be reversed for text content. For passwords, API keys, SSNs, payment numbers, and other security-critical strings, use solid-color redaction. Blur is acceptable only for casual privacy (faces in marketing shots, peripheral background detail). See references/redaction-safety.md.
Marks should read on any background	Use stroke + fill colors that contrast with the surrounding pixels, or add a contrasting outline to text. Yellow on a yellow page is invisible. The default style stacks a thick coloured stroke over the underlying pixels, never relies on transparency alone.
Coordinate origin is top-left	All (x, y) coordinates start from the top-left corner of the image. Y increases downward. Match the convention to whatever the source tool reports - browser DevTools and most screenshot tools agree on this.
One operation, one purpose	A single annotation does one thing. To layer marks, repeat flags or use a JSON spec - do not try to overload one operation.
Burn into a flat image	The output is a single-layer PNG or JPEG. No editable layers, no SVG re-edit path. If the user needs to iterate, they re-run the script with a new spec.

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Quick Start

Install (one-time, ask user first)

pip install --user Pillow

Pillow is the imaging library. Cross-platform, pure-Python install. Check first:

python -c "import PIL; print(PIL.__version__)"

Simple one-off: rectangle + arrow + label

python scripts/annotate.py input.png output.png \
  --rect 100,100,500,300 --rect-color red --rect-width 5 \
  --arrow 600,250,520,200 --arrow-color yellow \
  --text 600,260 "Click this button" --text-color white --text-bg black

That produces output.png with a red box around the region, a yellow arrow pointing into it, and a labelled callout next to the arrow.

Composition via JSON spec

For three or more marks, prefer a spec file:

[
  {"op": "rect",   "xy": [100, 100, 500, 300], "color": "red", "width": 5},
  {"op": "arrow",  "from": [600, 250], "to": [520, 200], "color": "yellow"},
  {"op": "text",   "xy": [600, 260], "value": "Click this button", "color": "white", "bg": "black"},
  {"op": "step",   "n": 1, "xy": [150, 150]},
  {"op": "step",   "n": 2, "xy": [350, 250]},
  {"op": "redact", "xy": [50, 600, 400, 640]}
]

python scripts/annotate.py input.png output.png --spec marks.json

Operations apply in order - later marks overlay earlier ones.

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Operations Reference

Rectangle - rect

Bounding box around an area. Outline only by default (no fill).

CLI flag	JSON key	Default
--rect x1,y1,x2,y2	{"op": "rect", "xy": [...]}	required
--rect-color NAME	"color": "red"	red
--rect-width N	"width": 5	4
--rect-fill NAME	"fill": null	none (outline only)

Arrow - arrow

Line with a triangular arrowhead at the end point. Points from (x1,y1) to (x2,y2) - the head is at (x2,y2).

CLI flag	JSON key	Default
--arrow x1,y1,x2,y2	{"op": "arrow", "from": [...], "to": [...]}	required
--arrow-color NAME	"color": "yellow"	yellow
--arrow-width N	"width": 6	6
--arrow-head N	"head": 20	20 (pixels, half-width of the head triangle)

Text label - text

Text with an optional filled background box for legibility on any underlying image. The position is the top-left of the text.

CLI flag	JSON key	Default
--text x,y "STRING"	{"op": "text", "xy": [...], "value": "..."}	required
--text-color NAME	"color": "white"	white
--text-bg NAME	"bg": "black"	black (set null for no background box)
--text-size N	"size": 24	24
--text-padding N	"padding": 8	8

Circle / ellipse - circle

Outline around a centre point. Useful for highlighting a single UI element.

CLI flag	JSON key	Default
--circle cx,cy,r	{"op": "circle", "center": [...], "radius": N}	required
--circle-color NAME	"color": "red"	red
--circle-width N	"width": 4	4

Numbered step marker - step

A filled coloured circle with a number inside, drawn in the order the user reads the image. Use for sequential tutorials ("first click here, then here, then here").

CLI flag	JSON key	Default
--step N x,y	{"op": "step", "n": N, "xy": [...]}	required
--step-color NAME	"color": "red"	red
--step-radius N	"radius": 22	22
--step-text-color NAME	"text_color": "white"	white

Stack multiple --step flags or list multiple step ops to enumerate a workflow.

Highlight - highlight

Semi-transparent coloured overlay over a rectangular region. Use to call attention to an area without obscuring its content. Defaults to a translucent yellow, like a marker pen.

CLI flag	JSON key	Default
--highlight x1,y1,x2,y2	{"op": "highlight", "xy": [...]}	required
--highlight-color NAME	"color": "yellow"	yellow
--highlight-alpha N	"alpha": 80	80 (0-255, lower is more transparent)

Blur - blur

Gaussian blur over a rectangular region. Not safe for security-critical content. Use only for casual privacy (faces, peripheral background detail, non-secret personal info).

CLI flag	JSON key	Default
--blur x1,y1,x2,y2	{"op": "blur", "xy": [...]}	required
--blur-radius N	"radius": 16	16

Redact - redact

Solid-color block over a rectangular region. Use this - not blur - for passwords, API keys, tokens, SSNs, payment numbers, or anything an attacker would reuse.

CLI flag	JSON key	Default
--redact x1,y1,x2,y2	{"op": "redact", "xy": [...]}	required
--redact-color NAME	"color": "black"	black

Crop - crop

Cut the image to a rectangular region. Applied first if present in the spec.

CLI flag	JSON key	Default
--crop x1,y1,x2,y2	{"op": "crop", "xy": [...]}	required

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Common Recipes

Bug-report screenshot: box the broken part, label it

python scripts/annotate.py bug.png bug-annotated.png \
  --rect 320,180,640,260 --rect-color red --rect-width 6 \
  --text 320,140 "Button stays disabled after valid input" --text-bg red

Tutorial: three numbered steps with descriptions

python scripts/annotate.py tutorial.png tutorial-annotated.png \
  --step 1 180,210 \
  --step 2 420,280 \
  --step 3 660,210 \
  --text 220,210 "Open the file menu" \
  --text 460,280 "Pick Export -> PDF" \
  --text 700,210 "Confirm the location"

Pre-share redaction: hide an API key and a session cookie

python scripts/annotate.py dashboard.png dashboard-shareable.png \
  --redact 80,420,580,452 \
  --redact 80,490,580,522

Privacy-light: blur a face in a marketing-shot

python scripts/annotate.py team.png team-anon.png \
  --blur 120,80,260,240 --blur-radius 24

(Use redact instead if the face must be unrecognisable in any forensic recovery.)

Highlight a paragraph in a documentation shot

python scripts/annotate.py docs.png docs-highlight.png \
  --highlight 60,300,720,420 --highlight-color yellow --highlight-alpha 90

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Picking Coordinates

The three reliable ways to find an (x, y) for a mark:

1. Browser DevTools elements panel - hover the element; the highlight shows pixel offsets in the page. Multiply by device-pixel-ratio if the screenshot was retina.
2. macOS Preview / Linux image-viewer / Windows Paint - open the screenshot, hover the target; most viewers show coordinates in the status bar.
3. A first dry run with a colour mark - drop a --rect 0,0,100,100 and binary-search outward until the box lands where you want. Wasteful but always works.

The coordinate origin is the top-left corner: x increases right, y increases down. Pillow, browsers, and OS screen-capture tools all agree on this.

See references/coordinate-cheatsheet.md for common picks and offsets.

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Quick Reference: Checklist

• Pillow is installed (python -c "import PIL")
• Input image exists and is readable
• Output path is different from the input - never overwrite the source
• Coordinates are within the image bounds (Pillow will silently clip otherwise)
• Colours are CSS-style names (red, yellow, #ff8800) - Pillow accepts both
• For sensitive data: redact not blur
• Final output viewed at full resolution to confirm marks land where intended

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Reference Files

Reference	Contents
redaction-safety	What is safe to blur vs requires solid redaction; recoverability research; common mistakes
coordinate-cheatsheet	Coordinate-picking tactics for typical screenshot dimensions; retina/DPR multipliers; offset patterns for arrows and labels

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Integration with Other Skills

Situation	Recommended Skill
Need to capture the source image first	web-screenshot - capture, copy to host, then run this skill on the host file
Generating a step-by-step tutorial	This skill's step operation plus the web-screenshot multi-viewport script for paired shots
Producing a PR or status report with annotated screenshots	report-writer - embed the annotated PNGs into the HTML report

Critical Rules

1. Never overwrite the source image. The output path must differ from the input path. Re-runs need the original.
2. Use redact for secrets, not blur. Blur is reversible for text content. Passwords, API keys, payment numbers, SSNs, JWT tokens, and anything an attacker could replay must be covered with a solid block.
3. Coordinates are top-left origin and pixel-based. Match the resolution of the image, not CSS pixels - if the screenshot is retina (2x), the coordinates are 2x what DevTools shows.
4. Operations apply in order. Later marks paint over earlier marks. Put redactions LAST in the spec so nothing in the source leaks through a partially-transparent overlay.
5. Output format follows the file extension. .png for lossless, .jpg for size-constrained. Annotations on a JPEG re-saved as JPEG will accumulate compression artifacts - prefer PNG when iterating.