How to scan a stamp or signature cleanly
Last updated: 2026-07-27
Whether a signature looks convincing in a PDF is decided at the scanning stage, not the editing stage. A clean source takes seconds to place; a bad one shows no matter how much you fuss afterwards. Since you will reuse the image for years, it is worth ten minutes of care up front.
Resolution: 300 DPI minimum, 600 DPI preferred
A typical handwritten signature is around 60 mm wide, or 2.4 inches. At 300 DPI that gives you roughly 700 pixels across; at 600 DPI, about 1400. A 25 mm company seal yields about 295 pixels at 300 DPI. Three hundred is enough for on-screen use and ordinary printing, but 600 preserves the soft taper at the end of each stroke and gives you headroom if you later need the mark larger.
Do not go to 1200 DPI: beyond the file size, you start resolving the paper's fibre texture, which shows up as scattered specks once the background goes transparent. 300 to 600 is the practical range.
Paper and pressure
Use white paper slightly heavier than standard copier stock. Thin paper lets whatever is behind it show through, which drags the background brightness down. If thin paper is all you have, stack three or four sheets underneath; it blocks show-through and stops the scanner lid's grey backing from tinting the page. Never use lined paper; the rules scan as sharply as your signature and are more work to remove than starting over.
For a rubber stamp or seal, ink the pad evenly, put two or three sheets underneath as a cushion so pressure spreads uniformly, and press straight down for three to five seconds. Any rocking motion produces a doubled, smeared outline. Stamp the sheet five or six times; picking the best impression is far faster than re-scanning.
Pen choice matters more than people expect
For signatures, use a gel pen or a fineliner, 0.7 mm or wider, in black. Ballpoints skip and produce thin strokes that scan grey rather than black — the single most common cause of a signature going semi-transparent when the background is removed. Avoid pencil; graphite is reflective and scans washed-out. Blue ink is fine and sometimes preferred, since it signals an original rather than a photocopy.
Sign slightly larger than the size you will actually use. Scaling a signature down sharpens it; scaling it up softens it.
Scanner settings
- Scan in colour, not black-and-white or greyscale. Bitonal modes crush a red seal into flat black and destroy the ink texture that makes it look real.
- Save as PNG or TIFF. JPEG leaves ringing artefacts along the ink edges, and those artefacts become a mottled halo when you make the background transparent.
- Turn off auto document enhancement and sharpening. These push contrast so hard they ring a white halo around every stroke, working against clean background removal.
- Nudge brightness up if the background scans grey. Transparency removal is a brightness test, so the closer the paper reads to pure white, the cleaner the result.
If you only have a phone
A phone camera is perfectly usable with two precautions. First, shadows: your hand and the phone cast a soft shadow you barely notice, but which darkens the paper enough to leave smears after background removal. Work near a window with indirect daylight, positioned so the light arrives diagonally. Shooting straight down under a ceiling fixture is the worst case.
Second, be careful with scanning apps. Document mode often binarises the image to pure black and white, which strips the colour out of a seal and hard-clips the fine strokes of a signature. Shoot with the plain camera app instead, hold the phone parallel to the paper, and fill the frame. Shooting at an angle turns a round seal into an oval that later correction never fully hides.
Afterwards
Crop away the surrounding paper and straighten any rotation — half a degree of tilt is visible once the mark sits on a document. Then open your PDF in StickPDF, drop the image on the page, and use 'Remove background' to make the paper transparent. Everything runs locally in the browser, so neither your signature nor the contract is uploaded anywhere.
Storage and security
Treat a good signature scan like a passport photo or a bank detail. Whoever holds the file can apply your signature to any document, and a transparent version is ready to use as-is. Keep it off shared drives and shared computers, and give it a name that does not advertise what it is.
One honest caveat: a scanned signature or seal applied to a PDF is a visual mark. It is not a certificate-based electronic signature and carries none of the tamper-evidence those provide. How much legal weight it holds depends on your jurisdiction, the document type, and what the parties have agreed.