How to redact a screenshot on a Mac

macOS has no one-click redact button, and the obvious methods leak. Real redaction removes the hidden pixels, it does not simply cover them. The safe way on a Mac is to draw a solid, fully opaque shape over the sensitive area, export a brand-new flattened image rather than saving over the original, then check the result before you share it. Blurring and pixelating are not redaction, and a black box that stays a separate layer is not either.

Redaction means removing, not hiding

The word gets used loosely, so start with the definition that matters. Redaction is the removal of information so it cannot be recovered. Hiding it behind a blur, a mosaic, or a box that sits on top of the original is obfuscation, and obfuscation can be undone. The NSA's own guide, "Redacting with Confidence," puts it plainly: sensitive information has to be actually removed from the file, not merely made hard to read. Everything below follows from that one idea.

The safe way to redact on a Mac

You can do this with Preview, with care.

1. Open the screenshot in Preview and show the Markup toolbar.
2. Preview has no blur or pixelate tool, and that is fine, because you should not use one anyway. Choose the rectangle shape instead.
3. Set its fill to solid black and its opacity to 100 percent, and cover the sensitive area completely. A marker or highlighter applies ink below full opacity, which leaves the pixels underneath readable when someone pushes brightness and contrast.
4. Flatten it. Go to File, then Export, and save a fresh PNG. Do not simply save over the original. Exporting a new file bakes the shape into the pixels and drops the editable annotation.
5. Strip metadata if the shot came from a camera or carries location data.

That is genuinely it, and it works. The catch is that every step is manual and easy to get half right, which is exactly how the failures below happened.

How to redact part of a screenshot, or crop it

To hide one region, cover it with the opaque shape above. To remove the edges of a shot, crop in Preview (select with the rectangle tool, then Tools, then Crop) or capture a smaller region in the first place with ⇧⌘4. One warning on cropping, covered next: crop by exporting a new file, not by overwriting the original, or the cropped-out part can survive inside the file.

Why the tempting shortcuts fail

This is the part almost every tutorial skips.

Blur and pixelation are reversible. In 2022 Dan Petro at Bishop Fox released a tool called Unredacter that reconstructs pixelated text. It renders each candidate word in the same font, pixelates the guess with the same settings, and matches it against the redacted image, walking along character by character. It builds on an earlier tool, Depix. Pixelation is deterministic and local, so there is a mapping to solve, and it is strongest on short, structured text in a known font, which is precisely the account numbers and codes people pixelate in screenshots. Petro's advice was blunt: no pixelization, no blurring.

The file can keep a copy you did not mean to keep. In 2023 a bug nicknamed aCropalypse (CVE-2023-21036) showed that Google's Pixel Markup editor, and Microsoft's Windows Snipping Tool, left the cropped or redacted portion of a PNG recoverable. When you edited a screenshot and saved over the original, the tools wrote the smaller new image without truncating the file, so the old data stayed after the end of the new image and could be reconstructed. Un-cropped photos and card numbers came back out of files people thought were clean. The lesson for any platform is the same: export a new file and check it, do not trust a save over the original.

A black box can be a layer, not a deletion. In January 2019, lawyers for Paul Manafort filed a court document with black boxes over sensitive passages, but the text underneath was still there. Anyone could select it and copy it out, which is how the press read the redacted material for the first time. The Ghislaine Maxwell deposition leaked a different way: an alphabetized word index at the back let journalists reverse the redactions, and one name was left uncovered on a page where it was redacted elsewhere. Same root cause each time. The covering mark was a separate object over intact data, or the data lived somewhere else in the file.

Check that it actually worked

Redaction is one of the few things worth verifying every single time. Open the file you are about to send, not the one you were editing. Zoom all the way in on the redacted area. Push brightness and contrast to their extremes and look for ghosting. Try to select and copy text over the blacked-out region, and you should get nothing. Confirm you exported a fresh, flat file. Thirty seconds here is the difference between hidden and gone.

How ScrubShot handles it

The manual route works, but it is fiddly and unforgiving, so I built ScrubShot to make the safe path the default. Press Fn + Space and it captures the whole screen with ScreenCaptureKit and opens it in an editor. You crop afterwards rather than fighting a drag selection.

The Scrub tool is the part I care about. A normal pixelate sets each block to the average of the pixels beneath it, which is the signal Depix and Unredacter exploit. ScrubShot does not do that. Each mosaic block is filled with the average of a few pixels sampled at random from across the whole selected region, so the block pattern is decoupled from whatever sat underneath. It looks like a redaction and keeps the rough colors of the area, but there is no per-block relationship to the original text to solve for. It reverses to nothing by design, and the scrub is baked straight into the image, so the original pixels are gone, not hidden on a layer.

From there you can add a marker stroke or a text label, crop, undo with ⌘Z, then Copy and Save. Finished images go to a dedicated folder at ~/Pictures/ScrubShot and to the clipboard, and the saved PNG contains only the scrubbed result.

The capture, scrub and share flow makes no network connections, so a screenshot with a password or a client's details in it never leaves your Mac. To be precise, the app does talk to a server for the free-trial check, license activation and update checks, and that request carries a hashed machine identifier and your license key, never any image data. ScrubShot runs on macOS 14 and later, on both Apple Silicon and Intel, and it needs Screen Recording and Accessibility permission to capture the screen and to see the Fn shortcut.

FAQ

Can you redact a screenshot on a Mac?

Yes, but there is no dedicated redaction tool. Open the screenshot in Preview, cover the sensitive area with a rectangle set to solid black at full opacity, then export a fresh flattened PNG rather than saving over the original. Avoid the blur and pixelate options, which are not safe for hiding text.

Is blurring or pixelating safe for hiding text?

No. Pixelated text can be reconstructed. Bishop Fox's Unredacter tool, and Depix before it, recover the original characters by matching re-pixelated guesses in the same font, and it works best on exactly the short, structured text people tend to pixelate, like account numbers and codes. Use a solid opaque cover, or a tool that destroys the pixels.

How do I black out text in a screenshot?

Cover it with a black rectangle at 100 percent opacity, then flatten the image by exporting a new file. A marker or highlighter applied below full opacity can leave the text readable when someone raises the brightness and contrast, and an unflattened shape can sit on a separate layer over intact text.

How do I redact just part of a screenshot?

Cover that region with an opaque shape as above. If you also crop, export a new file rather than saving over the original. Save-over-original bugs such as aCropalypse have left the cropped-out part of an image recoverable inside the saved file.

Does ScrubShot upload my screenshots?

No. The capture, scrub and share flow makes no network connections, so your screenshots never leave your Mac. The app contacts a server only for the trial check, license activation and update checks, and those requests carry a hashed machine identifier and your license key, never any image data.