Detecting forged signatures: tracing, photocopies and pasted images
In short Most forgeries are traced, copied from a genuine signature, pasted in from a file, or simply signed by someone else. Each leaves different traces. Unforged Nib looks for all four and says which one it found.
Four common kinds of forgery
- Tracing: someone draws over a genuine signature, through paper or on a screen.
- A copy: a photocopy or scan of a genuine signature, placed on a new document.
- A pasted image: a signature cut from one digital file and dropped into another.
- Someone else signing: a different person writes the name in their own way, or imitates the real signature freehand.
Each one leaves its own traces. None is proven by a single sign, so each finding is a reason to look closer.
Tracing
A tracer has to follow a line, so they move slowly and carefully. The strokes come out slower and more even than the person’s usual hand. Starts and ends are often blunt, with small pauses.
Unforged Nib compares the strokes with the person’s references. When they are slower and more uniform, its reason says so: “possible tracing”.
A traced signature is never approved: it gets FLAG, or FAILED if the rest of the evidence is against it too. Either way, a person takes a look.
Photocopies and scans of a real signature
Nobody signs exactly the same way twice. So a signature that lines up almost perfectly with one of the references is suspicious. It may be a photocopy, a scan or a careful tracing of that reference.
Unforged Nib checks each signature against the references for this. A near-exact overlay gets the reason “possible photocopy, scan or tracing of it” and the verdict FAILED. FAILED always goes to a person.
Pasted images
On a digital document, a signature can be cut from one file and pasted into another. The background around it often gives it away: a slightly different colour, noise or edge from the rest of the page.
Unforged Nib looks at the background around each signature. When it differs from the page, the reason reads “possible pasted image”. The signature is never approved: it gets FLAG, or FAILED if the rest of the evidence is against it too.
Someone else signing
The most common forgery is the simplest: another person signs. Their letter shapes, stroke flow and proportions follow their own habits, not the named person’s.
This is where comparing with the person’s own references matters most. When the evidence points clearly to another hand, Unforged Nib gives the reason “Strong evidence of a different writer” and the verdict FAILED.
Why the person’s own references matter
A forger who practises can copy the look of a signature well. What is hard to copy is how one person varies from one signature to the next: their pace, their pen lifts, the letters they always simplify.
Comparing with several of the person’s own references captures that variation. It also catches the opposite case, a signature that is too perfect. More references narrow the band around the probability, so the answer is more certain.
What software cannot see
Some evidence lives only in the original. Indentations in the paper, the ink itself and true pen pressure need the physical document and a forensic document examiner.
A phone photo or a poor scan can also hide detail. Unforged Nib returns UNREADABLE when an image is too poor to check, and that result is free. Ask for a better image rather than guessing.
Putting it into practice
- Enrol genuine references for each person, ideally several.
- Check every signature against them, not against a general idea of a real one.
- Send FLAG and FAILED to a trained reviewer with the reasons attached.
- Keep the reasons, policy and version with the record.
For the basics of checking by eye, read how to verify a signature. To see every check in one place, go to how Unforged Nib works.