Original lab · Privacy workflow

Can declared redaction zones be verified after the PNG is encoded again?

The lab uses a fully synthetic 640×360 source drawing with three invented strings, three in-bounds rectangles, and one out-of-bounds rectangle. It separates coverage evidence from the much harder question of whether the reviewer found every sensitive region.

Worked sample, not a live redaction result.The source SVG and coordinate JSON are fixture generators. The canonical tool accepts PNG, JPEG, or WebP—not SVG—and must be run to create and verify an actual redacted PNG. No real account, token, person, or support ticket is shown.

Run Screenshot Redaction Proof Studio Read the workflow guide Verify receipt + artifact bytes

Benchmark design

Accepted coordinate set

Three rectangles remain within a 640×360 image and are intended to cover the synthetic email, token, and reference strings after the source is rendered to PNG.

Rejected coordinate set

A rectangle begins at (620, 340) with size 80×40. Its right and bottom edges exceed the declared image dimensions and must not be silently clipped.

Method

Render the passive SVG fixture to a PNG outside the tool, then load that PNG. SVG remains rejected as an active document format.
Add the three declared regions manually and confirm their labels and coordinates.
Rasterize solid fills into a new canvas rather than placing a removable visual overlay.
Encode a new PNG, decode those exact bytes, and verify dimensions, fully opaque pixels, and uniform color inside every accepted rectangle.
Inspect PNG chunks for sensitive metadata, hash the exported bytes, and visually review the entire image before sharing.

Fixture commands and hashes

On macOS, this command creates an accepted PNG input from the passive source. The fixture hashes below cover the checked-in source and coordinate bytes; the workbench receipt must cover the PNG and exported artifacts from the actual run.

sips -s format png \
  app/fixtures/flagship-editorial-20260713/screenshot/safe-synthetic-screenshot-source.svg \
  --out /tmp/fasttool-safe-synthetic-screenshot.png

shasum -a 256 app/fixtures/flagship-editorial-20260713/screenshot/*

safe-synthetic-screenshot-source.svgbf54a471127ed73367d85b1cacf6c00fa936db191c252aa1f51340a365465c89
accepted-zones.json8c8e9a7e7c4fee1c5af416203f989aea8b62429976e5e7b3580eb96a9e2eb963
rejected-zone.jsonb7f0403ef35ad87521cdccaa0beec40f64db4ff01ae849fdd7794cba7611b56f

Deterministic fixture observations

Case	Declared image	Zones	Geometry observation	Expected handling
Accepted zones	640×360	3	All rectangles have positive size and remain in bounds.	Eligible for pixel verification
Rejected zone	640×360	1	Right edge 700 and bottom edge 380 exceed the image.	Reject before export

Geometry alone cannot prove that the correct content was selected. A live PASS requires re-decoded output-byte checks and a human whole-image review.

Limits and privacy

Limits

OCR is intentionally disabled; the tool cannot discover an unselected secret.
Uniform pixels prove declared rectangle coverage, not legal sufficiency or contextual anonymity.
A receipt cannot prove that the original was deleted or that a recipient did not retain another copy.

Privacy boundary

Use synthetic or properly authorized images on a trusted device. The canonical tool keeps image pixels and generated artifacts in browser memory, but local malware, extensions, screen recording, and user sharing remain outside its control.

Official sources

Corrections

Report a coordinate, source, hash, or method error to [email protected] with the exact issue and evidence. FastTool is the accountable publisher; material corrections appear in the changelog. Reviewed 2026-07-13.