Redact an image

Every box you draw is applied to a canvas holding the image at full size, and the export is that canvas. So what leaves the page is a new picture in which those pixels have already been replaced — there is no layer to peel off, no original underneath, and no metadata, because a canvas carries none.

The three methods are not equally safe, and the page ranks them on purpose. A solid block replaces the area with flat paint: the information is gone, and nothing can bring it back. Pixelation averages each cell down to one colour — with a cell that is large compared to the text underneath, that is a real loss, but coarse text pixelated with a small cell has been recovered before by trying every candidate string and comparing the result, so it is not the tool for a password or an account number. Blur is the weakest: it is a reversible operation in principle, and a light blur over sharp text is close to an invitation. If the point is that nobody should read it, use the block; the other two are for when you want the shape of the thing to stay visible.

The blur is a box blur run three times, which is a close and much faster stand-in for a Gaussian; the strength slider is the pixel cell for pixelation and the radius for blur, in the image's own pixels. Undo removes the last box, Clear starts again — both rebuild the picture from the original rather than trying to paint over themselves.

JPEG out means the whole picture is compressed again, so PNG is the default here; a screenshot stays sharper as a PNG anyway. An animated GIF is flattened to its first frame. The file is read in this tab with FileReader, the page makes no network requests, and nothing you drop is stored; the Dark button keeps its own setting in this browser's local storage.