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How to redact a screenshot on Mac
By Ziad Ziadeh, Snapline’s developer · Published 19 September 2026
The short version
- Cover sensitive text with a solid box, not blur or pixelation: security researchers have published a tool that turns pixelated text back into the original. Then make sure the box is merged into the image, not floating on top of it.
- Free route: open the screenshot in Preview, draw a rectangle from the Markup toolbar, fill it black, and save. Apple notes that annotations on a saved image can't be edited or removed afterwards, which is exactly what you want here.
- To find what needs hiding, Snagit and Snapline both have a Smart Redact that scans the image for you. Snapline's runs on device, also looks for API keys, tokens and IBANs, and can run on every capture.
Blur and pixelation are not redaction
A redaction has to remove the information, not just make it hard to read. Blur and pixelation look redacted, but each pixelated block is still an average of the pixels underneath it, and that is enough to work backwards from. The security firm Bishop Fox published a tool called Unredacter that does exactly that for pixelated text, in a post titled "Never, Ever, Ever Use Pixelation for Redacting Text"; its advice is black bars.
So a redaction that holds up needs two things. It covers the text with something opaque (a solid box, or cropping the text out altogether), and it is merged into the image's pixels, so the file you share no longer contains what was underneath. A black rectangle that is still a separate, movable object in the file fails the second test even though it looks perfect.
| Method | Finds sensitive text for you | Ways to cover it | Merged into the file you share | Cost model |
|---|---|---|---|---|
| Preview Markup (an image) | No | Filled shapes; crop | Yes, when you save | Free, preinstalled |
| Preview Redaction (text in a PDF) | No | Bars over the text you select | Yes, once you close the document | Free, preinstalled |
| Snagit Smart Redact | Yes: addresses, card numbers, dates, emails, faces, IP addresses, phone numbers, Social Security numbers, URLs | Blur, pixelation, black bars | When you finalize the image | Yearly subscription |
| CleanShot X | Not on its feature list | Pixelate (randomized), blur (secure or smooth), filled rectangle | Not stated on its site | Paid: one-time license for the core app |
| Shottr | Not on its feature list | Pixelate; remove an object; a text mode that hides text | Not stated on its site | Free to use; optional license |
| Snapline Smart Redact | Yes: emails, phone numbers, URLs, street addresses, card numbers, IBANs, JWTs, API keys, hex secrets; opt-in faces and people | Pixelate (the default), blur, solid box | Yes, baked in; the original is kept so it can be restored | One-time license; free to try |
The free route: a solid box in Preview
Preview, which comes with every Mac, is all you need for an occasional redaction. Its Markup tools draw shapes with a fill color, and on an image file that is the whole job:
- Open the screenshot in Preview. If you want to keep an unredacted copy, choose File → Duplicate first, because the next save is permanent.
- Click the Markup button if the Markup toolbar isn't showing. Clicking the thumbnail that floats in the corner right after you take a screenshot opens it for editing too.
- From Shapes, choose the rectangle and drag it over the text. Set its fill color to black (and its border to match), and cover every line, including the edges of letters.
- Choose File → Save. Apple's guide is explicit that once you save an image file, you can't edit, move, or delete its annotations: the box is now part of the pixels.
If the sensitive part sits at an edge of the shot, crop it away instead. A crop leaves nothing behind to recover.
PDFs are different
The same box drawn on a PDF behaves the opposite way. Apple's guide to annotating a PDF says File → Save keeps annotations editable, so anyone who opens the file can drag your black rectangle off the text. For a PDF, use Preview's Redaction Selection tool on the text itself, which becomes permanent once you close the document, or flatten the annotations with File → Print → Save as PDF. Apple also notes that a table of contents entry pointing at redacted text is not removed. If you pasted a screenshot into a PDF to annotate it, redact the screenshot as an image first.
Where the free route stops
Preview covers what you point at, and nothing else. Every email address, account number and API key has to be spotted by eye, which is exactly where redaction fails in practice: the second copy of the token in a log line, the address in a browser tab, the face in a video-call thumbnail. It also only runs when you remember to run it. And if iCloud Drive's Desktop & Documents Folders option is on, your Desktop is stored in iCloud Drive, so the unredacted screenshot may have synced before you opened it. For anything sensitive, change where screenshots save (the Screenshot app's Options menu, ⇧⌘5), or hold Control to copy the capture to the clipboard and redact before saving.
Screenshot apps with redaction: Snagit, CleanShot X, Shottr
Screenshot apps put redaction one click from the capture, and two of them go further and look for the sensitive text themselves. Each is described from its maker's own site:
Snagit
Snagit's Smart Redact lives in its Blur tool: one button scans the image for addresses, credit card numbers, dates, email addresses, faces, IP addresses, phone numbers, Social Security numbers and URLs. You choose which types to cover and whether to use blur, pixelation or black bars, and you can adjust the result before finalizing. It is the one on this page that also looks for dates, IP addresses and Social Security numbers. Snagit is a yearly subscription, with one license for Windows and Mac.
CleanShot X
CleanShot X's annotation tools include pixelation it randomizes for better security, a blur with secure and smooth options, and a filled rectangle. Its feature page doesn't list automatic detection, so finding what to cover is up to you. It is paid: a one-time license for the core app.
Shottr
Shottr, free to use, can pixelate a region or remove an object so it looks as if it was never there, and has a text mode that hides text without disturbing the pixels around it. Like CleanShot X, it leaves the finding to you.
Which one to use
- Free, now and then: Preview with a solid box, or Shottr.
- Personal data at work (addresses, Social Security numbers, IP addresses), on Windows and Mac: Snagit.
- Terminals, dashboards and settings pages full of keys and tokens, or redaction on every capture without thinking about it: Snapline, below.
Automatic, on device: Snapline's Smart Redact
Snapline's Smart Redact scans a capture and covers each match with an ordinary redaction that you can delete on its own. Its text detectors find email addresses, phone numbers, URLs, street addresses, card numbers, IBANs, JWTs, API keys and hex secrets, and two opt-in visual detectors find faces and people. All detection runs on your Mac.
- Capture with ⌥⌘S (rebindable), then press Redact on the Quick Access card. Smart Redact runs and bakes the boxes into the capture, which wears a badge on the card and in History and lands on the clipboard ready to paste. Press Redact again to bring the original back.
- Or open the capture in the editor, run Smart Redact there, and delete any box you don't want before you save.
- To cover exactly some characters, use the Select Text tool: select the text right on the image and press R for one redaction per line.
- Switch on automatic redaction to run Smart Redact after every capture. The un-redacted original is then kept in Snapline's own Application Support storage rather than your screenshots folder, so raw pixels never land in a folder that may sync to a cloud service.
One thing to set: redactions default to pixelation, which reads clearly as redacted. For text that must not be recoverable, switch the style to a solid box, the one style that cannot be reversed by image analysis. Snapline is free to try in full for 14 days (after the trial, capture unlocks with a one-time license: no subscription, no account) and requires macOS 14 or later.
Questions
Is blurring or pixelating a screenshot enough to hide information?
Not for text that matters. Blur and pixelation keep part of the original signal, and Bishop Fox's Unredacter tool turns pixelated text back into readable words. Cover the text with a solid box that is saved into the image, or crop it out.
How do I black out text in a screenshot on Mac for free?
Open the screenshot in Preview, show the Markup toolbar, draw a rectangle over the text, set its fill color to black, and save. Apple notes that annotations on a saved image can't be edited, moved or deleted afterwards. Choose File → Duplicate first if you want to keep an unredacted copy.
Can someone remove a black box from my screenshot?
Not from a PNG or JPEG where the box was saved into the pixels. They can from a PDF where the box is still an annotation: in Preview, use the Redaction tool on the PDF's text, or flatten it with File → Print → Save as PDF.
Which app redacts screenshots automatically on Mac?
Snagit's Smart Redact finds addresses, card numbers, dates, emails, faces, IP addresses, phone numbers, Social Security numbers and URLs. Snapline's Smart Redact finds emails, phone numbers, URLs, street addresses, card numbers, IBANs, JWTs, API keys and hex secrets on device, with opt-in face and person detection, and can run after every capture.
Could an unredacted copy of my screenshot still exist?
Yes, if it synced first. With iCloud Drive's Desktop & Documents Folders on, the Desktop is stored in iCloud Drive, and the Desktop is where macOS saves screenshots by default. Change the save location in the Screenshot app's Options menu, or copy the capture to the clipboard and redact before saving.