Redact guide
How to hide personal information in a screenshot
Cover each detail with a solid, opaque box and save a new copy of the picture made from its pixels. Don’t rely on blur, a highlighter or quick pen strokes: they can often be undone or seen through. Redact does it free in your browser, and the screenshot is never uploaded.
Why blurring and scribbling aren’t safe
Most screenshot editors offer a pen, a highlighter, a blur or a pixelate brush. They look convincing on a phone screen, but several of them can be undone or seen through:
- Blur. A blur mixes nearby pixels rather than removing them. Light blurs on text can often be read back, and for short, predictable things (a card number, a postcode, a name from a known list) someone can blur every candidate the same way and see which one matches.
- Light pixelation. Large, chunky blocks over a face are fine. Small blocks over text keep the rough shape of each letter, and the same guess-and-compare trick works on them.
- Highlighters and thin pens. Many markup highlighters are partly see-through. Brighten the picture or raise its contrast and the words underneath come back. A few quick pen strokes usually leave gaps between them.
- Cropping in an editor that keeps the original. In 2023 a bug nicknamed “aCropalypse”, in Google Pixel’s Markup editor and Windows’ Snipping Tool, left the cropped-away part of a picture inside the saved file, where it could be recovered. Both were fixed by updates, but older saved copies can still hold the hidden part. The lesson: the safest copy is one saved again from its visible pixels only.
The fix for all four is the same: cover what you want hidden with a solid, opaque box, then save a new copy of the picture made from its pixels.
What to look for before you share a screenshot
The thing you meant to show is rarely the problem. It’s everything around it. Check these before you send:
| Where | What it can give away |
|---|---|
| Chats and group names | Other people’s names, phone numbers and profile pictures, not just yours |
| Notification banners | A message preview or a one-time code that arrived while you took the shot |
| Browser address bar and tabs | Your email address, an order number, or a link with a private token in it |
| Emails | Full addresses in the To, From and Cc lines, signatures with phone numbers |
| Tickets and boarding passes | The barcode or QR code, which can hold your booking reference and name even when the text is covered |
| Bank and shopping apps | The last digits of a card, a sort code, a balance, a delivery address |
| Photos of documents | Dates of birth, ID numbers, signatures, and a second page peeking out underneath |
| Photos of places | House numbers, car number plates, school uniforms, a street sign in the window |
How to black out a screenshot, step by step
These steps use Redact, which runs in your browser on a phone or a computer. The picture is never uploaded.
- Open the picture. Choose a JPG, PNG, WebP or HEIC file (an iPhone photo). It opens on your device.
- Draw a box over each detail. On a computer, drag across what you want hidden. On a phone, turn on ✎ Draw first, so dragging draws instead of scrolling. A screenshot is a picture, so Redact can’t read or search its words: you box them by eye.
- Be generous. Cover the whole line, including the tops of tall letters and the tails of letters such as g and y. A box that stops at the middle of a line can leave enough of each letter to guess the word.
- Pick a style. Black is the usual sign that something was removed. White blends into a white page, so nobody can see where something was. Pixels (photos only) uses strong, chunky blocks, which suit faces and number plates. For text, stay with black or white.
- Fix mistakes. Tap a box to remove it, or use Undo.
- Save. Redact draws your boxes into the picture and saves a new copy, named
…-redacted. A PNG stays a PNG; JPG, WebP and HEIC are saved as JPG. - Look at the saved copy. Open it, zoom in on each box, and check nothing shows at the edges before you send it.
Because the new copy is made from the picture’s pixels, the original file’s hidden details (where and when it was taken, and the phone that took it) aren’t carried over. If you only want to see or remove a photo’s location without changing the picture, use Image Tools’ Photo info instead.
Black box, white box or pixels?
| Style | Best for | Watch out for |
|---|---|---|
| Black | Text, numbers, codes, anything in a document | Shows that something was removed, and roughly how long it was |
| White | Screenshots on a white background, when a black bar would distract | On a coloured background it stands out as clearly as black |
| Label | Documents where the reader should know why (“Redacted”) | Needs a box tall enough for the word to fit |
| Pixels | Faces, number plates, people in the background | Never use it for short text such as a card number: blocks can be guessed back |
Redact’s pixel blocks are large on purpose: each box is cut into about seven blocks across its longest side, never smaller than 12 pixels. That hides a face, but it is still not a replacement for a solid box over words.
When the screenshot is really a document
If you have the original PDF (a bank statement, a payslip, a contract), redact the PDF rather than a screenshot of it. The recipient gets a proper document, and Redact can do much more with real text: find every place a name appears, find email addresses, phone numbers, card numbers, IBANs, sort codes and account numbers for you to review, and check the saved file for anything you missed. How to redact a PDF properly walks through it, and how to check a PDF is properly redacted covers the tests to run afterwards.
Common mistakes
- Hiding your own name but not the other person’s. A screenshot of a conversation exposes everyone in it.
- Covering the number but not the code. The barcode on a parcel label or ticket can carry the same details.
- Sending the original by accident. Redact saves a new file with
-redactedin its name. Attach that one, and delete the original from the chat if you sent it first. - Trusting a blur on text. Use a solid box for words and numbers, always.
- Forgetting the reflection. Screens, windows and glasses in a photo can show a second copy of what you hid.
Questions
Can a blurred screenshot be unblurred?
Sometimes. Blur mixes pixels rather than removing them, so light blurs on text can be read, and short predictable text such as numbers can be matched by blurring guesses the same way. A solid box can’t be reversed, because the pixels under it are replaced.
Is pixelating text safe?
Not for short or predictable text. Small blocks keep the rough shape of each letter. Use strong pixel blocks for faces and number plates, and a solid black or white box for words and numbers.
How do I black out part of a photo on my iPhone?
Open the photo in Redact in Safari, turn on ✎ Draw, drag a box over each detail and save. HEIC photos open as they are, and the redacted copy is saved as a JPG without the photo’s location and camera details.
Does Redact upload my screenshot?
No. Redact runs in your browser and the picture never leaves your device. It also works offline once it has loaded.
Can Redact find personal details in a photo automatically?
No. A photo or screenshot is pixels, not text, so Redact can’t read it: you draw the boxes yourself. Automatic finding of emails, phone numbers and account numbers works in PDFs that contain real text.