Blank out a picture

Pixelating is not removing

A pixelated or blurred face has not been deleted, it has been recalculated. With a coarse enough grid and enough effort, something can be brought back out of such an area — especially for text and numbers, where the set of possible originals is small. An eight-character number plate is exactly that case.

No filter is laid over the area here. It is overwritten in black and the picture is then rebuilt, so the original pixels are no longer present.

What else a photograph gives away

Besides its pixels a photograph carries data most people never think about: where it was taken as a GPS coordinate, the date and time, the camera model and serial number, sometimes the owner's name.

Two of those survive even a metadata strip: the small preview inside the EXIF block, which often still shows the uncropped or unedited original, and extra images some cameras append behind the actual photograph. Both go here, because the result is written from the pixels rather than edited out of the source file.

Remains after the end of the file go with them — the gap through which cropped screenshots were recoverable on Android phones in 2023.

The check after saving

Once written, the finished file is taken apart again and read. If anything besides the pixels turns up — or anything sits past the end marker — the file is reported rather than saved.

The result is a PNG. The EXIF orientation is applied first, so a portrait photograph does not come out on its side.

What this is for

Selling a car without handing over the registration. Passing on a photograph with someone in it who would rather not be. Sending a receipt that shows an address or an account number.

A PDF has its own tool, because what has to come out of one is different: text, fonts, form fields, earlier revisions.