Ink, paper and light decide the outcome
Dark blue or black ink on unlined white paper is the combination that survives everything downstream. Ruled paper puts horizontal lines through the image that the encoder has to store and a verifier has to look past. Coloured or cream paper narrows the contrast between ink and background before anything has even been compressed.
A gel pen or a fountain pen lays down a denser line than a dry ballpoint. If the only pen to hand is running out, the strokes will already be broken in the original and no amount of care afterwards will rebuild them.
Scanning, if you have the option
Scan in colour rather than black and white. A black and white scan makes a hard decision about every pixel at the moment of scanning, and it tends to eat the thin tapering ends of strokes. Colour keeps them, and the compression afterwards is gentler about what it discards.
Around three hundred dots per inch is plenty. Higher settings produce an enormous file that then has to be thrown away again, and the extra detail was never going to be visible in a signature box on a form.
Why the limit is easy to meet
Once the frame contains only the signature, twenty kilobytes is rarely a fight. A tightly cropped signature at a sensible width often lands under the limit at high quality, which means you keep the crispness rather than trading it away. If yours does not, the frame still has background in it.
Questions
- Is 20KB better than 10KB if both are allowed?
- Yes, use the larger allowance when the form permits it. More bytes mean the encoder keeps more of the fine detail at the ends of strokes, and a signature that is verified by eye against a physical specimen benefits from every bit of that. There is no advantage to submitting a smaller file than the form asks for.
- Can I sign on a phone or tablet screen instead?
- Only if the form allows a digitally drawn signature, and many do not because the stroke looks visibly different from a pen. Where it is allowed, draw slowly with a stylus rather than a fingertip and export on a white background. Check the instruction page before assuming it will be accepted.
- Does the background need to be pure white?
- It does not have to be perfectly white, but it does need to be even. A uniformly off-white page compresses cleanly and reads fine. A page with a shadow gradient across it does not, because the encoder treats the gradient as detail worth keeping and spends the budget there rather than on the ink.