Cover something up, properly
A blurred account number can often be read back. A solid block cannot.
Hiding something in a picture goes wrong in two well-documented ways. Drawing a shape over text in a document leaves the text in the file, selectable from behind the box. Blurring or pixelating looks decisive but is a reversible transform: against a known alphabet, such as an account number or a licence plate, the original can often be recovered by searching for the input that blurs to the same output. This replaces the pixels themselves, and defaults to a solid block because that is the only one of the three with nothing left to recover.
How to use it
- Drop in the image. It is decoded in the page and never uploaded.
- Drag a box over anything that should go. Add as many as you need.
- Pick how it is covered. Solid is the safe answer.
- Apply and download. The regions are redrawn at full resolution.
Which covering to choose
- Solid block replaces the pixels outright and cannot be undone.
- Pixelate looks censored but is reversible in principle.
- Blur is the softest looking and the least secure of the three.
- For anything with text or numbers in it, use a solid block.
Questions
Can a blurred or pixelated image be un-blurred?
Often, yes, when the hidden content is drawn from a small set of possibilities. Both are reversible transforms, so an attacker can blur every candidate — every account number, every plate — and look for the one that produces the same output. This has been done to real redactions. A solid block has no such weakness because the original pixels are simply gone.
Why not just draw a black rectangle in an image editor?
On an image that is the same thing, as long as you export a flattened file. The classic failure is doing it in a document or a PDF, where the box is an object drawn on top and the text underneath is still there to be selected, searched or copied out.
Does the redaction survive editing afterwards?
Yes. The output is a new image whose pixels have been replaced, so there is no layer to remove and no original underneath. It is not an overlay.
Is the metadata removed too?
No, that is a separate job. If the photograph also carries GPS coordinates or a camera serial number, run it through Remove Metadata afterwards, since covering a face in the picture does nothing about the location recorded in the file.
Does the image get uploaded?
No. It is decoded, drawn and re-encoded in this tab. There is no upload endpoint to send it to, which for a tool whose whole job is sensitive pictures is rather the point.