Image Redactor

How it works

Each box you drag is drawn straight onto the canvas's pixel data with fillRect(), on top of the loaded image — it isn't a separate movable layer sitting over the picture. Undo works by keeping the list of box coordinates separately and re-rendering the original image plus whatever boxes remain, so you can remove a mistake freely before exporting. Once you export, canvas.toBlob() reads the canvas exactly as it looks on screen, so the pixels under each black box are gone from the output file, not just hidden.

FAQ

Is the black box just an overlay someone could peel back off the image, like in some infamous PDF redaction failures?

No — the rectangle is painted directly into the canvas's pixel data, and the exported file is generated from that same canvas, so the original pixels underneath are fully overwritten and unrecoverable in the downloaded image.

Can I still undo a box after I've drawn several more on top of it?

Yes — undo removes the most recently added box from the list and redraws the original image plus every remaining box from scratch, so boxes can be removed in reverse order without disturbing the image itself, right up until you export.