Transparent signature from a photo

How signature mode works

A signature is dark ink on lighter paper, which simple image processing handles better than an AI model. Signature mode converts the photo to greyscale and compares every pixel with the average of its neighbourhood (an adaptive threshold). Ink is darker than its surroundings; paper, even shaded paper, is not. That is why a phone's shadow across the page, or uneven light from a desk lamp, does not turn into a grey smudge in the result. The ink is then recoloured, navy by default, with smooth anti-aliased edges, and everything else becomes transparent.

Getting a good signature photo

1. Sign on plain white paper with a dark pen. A felt-tip or gel pen gives a bolder line than a fine ballpoint.
2. Photograph it in daylight, holding the phone parallel to the page so the signature is not skewed.
3. Fill the frame with the signature, with a little margin.
4. Load it here. If faint strokes disappear, raise Sensitivity; if paper texture appears, lower it.
5. Pick an ink colour (black or blue are conventional), then download the PNG.

Using it in a PDF

A transparent PNG sits cleanly over the signature line of a form. Most PDF readers and editors can place an image. If yours cannot, the site's PDF sign tool will do it in the browser. A pasted signature image is a visual signature: it shows that you signed, but it is not a cryptographic digital signature, and some organisations require one or a wet-ink original. Check what the recipient accepts.

Keep it safe

A clean image of your signature is valuable to fraudsters. Because this tool runs entirely in your browser, the signature is never sent to a server, but once you have the file, store it as carefully as you would a scan of your licence.