What is signature verification software?
In short Signature verification software checks whether a signature was made by the person it claims to be from. Good software compares it with that person’s own reference signatures and explains its answer, so a person can act on it.
A definition
Signature verification answers one question: did this person make this signature? Software does it by comparing the questioned signature with genuine signatures by the same person.
It is different from finding a signature on a page, which is only the first step. It is also different from checking a digital signature, which is a cryptographic seal on a file, not handwriting.
Images or live capture
Some tools work from images: a scan, a photo or a PDF of a signed document. Others capture the signature live on a pad or screen, with the timing of each stroke.
Unforged Nib works from images and PDFs. It reads forms, scans, phone photos, PDFs, TIFFs and ZIP archives, up to 50 MB and 200 pages.
How comparison against references works
A general idea of what a genuine signature looks like is not enough. People sign in very different ways. So good software compares each signature with that person’s own references, enrolled once.
Unforged Nib runs five steps on every document:
- Find: it locates the signature on the page, even on forms, scans and phone photos.
- Clean: it lifts away ruling lines, stamps and background, so only the ink is left.
- Compare: it measures letter shapes, stroke flow and proportions against the person’s references, and how much that person usually varies.
- Score: it turns the evidence into a calibrated probability from 0 to 1, with a band showing how sure it is.
- Explain: it gives one of six verdicts and the reasons behind it.
What a verdict with reasons looks like
A bare score leaves you to decide what it means. A verdict tells you what to do, and the reasons tell you why. Unforged Nib returns one of six:
- AUTO APPROVE and APPROVE: likely genuine. File it.
- FLAG: inconclusive. A person takes a look.
- FAILED: strong evidence of a different writer, or a copy of a reference. Always a person.
- UNREADABLE: the image is too poor to check. Ask for a better one.
- NO SIGNATURE: nothing to check.
A reason reads like “Compared against 3 references” or “Strokes are slower and more uniform than the references (possible tracing)”. Each result also records the policy and version that produced it, so you can show an auditor how it was decided.
Where people stay in charge
Software should do the first pass, not the final call on a rejection. FAILED always goes to a person. It is never an automatic rejection. FLAG goes to a person too.
You set the policy: where approve begins and where fail begins. A stricter policy sends more to your reviewers. A looser one lets more through.
Where it is used
Signature verification earns its keep wherever a signature decides something and there are too many to check by eye:
- Sign-ups, e-signatures and KYC, where a platform onboards thousands of people.
- Mandates, consent forms and contracts, checked against the signatures a back office already holds.
- Proof of delivery, photographed on a driver’s phone at the door.
- Application forms and scanned archives, checked in bulk.
In each case the software does the first pass on every signature, and people spend their time on the few that need them.
What it cannot do
- Judge paper, ink or pen pressure you cannot see in an image. That needs the original and a document examiner.
- Check a signature with nothing to compare it with. It needs at least one genuine reference.
- Read every script. Unforged Nib reads signatures in Latin script today.
To weigh up tools, see what to look for in a signature verification API and the glossary.