3D Holograms Detect Fake Signatures

By Roland Piquepaille

Several sources reported last week that a new technique that produces 3D holograms of handwriting could be used to detect fake signatures on checks, credit card receipts or other important handwritten documents. Here are pointers to Nature, Scientific American or BBC News Online. Instead of using 2D techniques to look at the sequence of pen strokes in a signature, this new method is based on 3D micro-profilometry which permits to translate the writing into an image showing dips and furrows of the sample so that anomalies can be detected. If you plan to imitate your spouse's signature, beware! Forensics have a new and very efficient tool. As an example, for the use of ballpoint pens on normal paper, the success rate was 100%.

Nature describes the problem and its solution.

Suspect signatures are usually analysed by expert graphologists, who compare the appearance of different letters in a name with a verified original. However, they are restricted to looking at flat, two-dimensional writing, and good forgeries can sometimes slip through the net.

The new three-dimensional analysis reveals the sequence in which each pen stroke was made on the page. The technique also highlights differences in the pressure applied by the writer as they marked the page. Such pressure differences are extremely difficult to mimic.

Let's turn to BBC News for more details.

Conventionally, handwriting has been analysed by forensic experts in 2D, looking at the sequence of pen strokes in handwriting, like a signature.

But this is not entirely accurate, because the exact sequence of strokes is not always clear and can vary.

"Using virtual reality and image processing, it is possible solve two of the most difficult problems in graphology: strokes superposing and strokes direction.

"These, in particular in case of same inks, are not detectable in a objective way with the traditional methods," Lorenzo Cozzella, part of the research team, told BBC News Online.

Here is a an example of "profilometric acquisition by means of conoscopic holography. These strokes were made by a BIC pen on common paper. The investigation area is about 5 mm × 5 mm. (a) 3D view of the strokes' profile. It is possible to note the regularity in the (S) line. (b) 3D view of the strokes' profile. The presence of bumps is evident. (c) 3D view with a mirror along the z-axis."

The research work has been published by the Journal of Optics A: Pure and Applied Optics in its Septemebr issue under the name "Superposed strokes analysis by conoscopic holography as an aid for a handwriting expert." Here are two links to the abstract and the full paper (free registration needed, valid for 30 days, PDF format, 6 pages, 320 KB). The above images come from this paper.

How is this technique working? Surprisingly well, according to Nature.

To test their system, the scientists used a database of 126 letters, each written by a different author. In almost 90% of the cases they tested, the author of a particular letter could be identified by comparing details of how their pen strokes crossed with a set of verified writing samples. For ballpoint pens on normal paper, the success rate was 100%.

If you want to see the detailed results, please read the research paper mentioned above. Below is a diagram, also extracted from this paper, showing the equipment used by the researchers.

This is a basic conoscopic range finder set-up used by the Italian researchers.

And now, what's next?

The scientists say that the system could also be used to study ancient documents that may be too precious to analyse in other, potentially damaging ways. The equipment is rugged and portable, and could be taken into museums to do analyses on site. "The technique does not damage the sample," explains Schirripa Spagnolo.

Sources: Mark Peplow, Nature, August 10, 2004; Sarah Graham, Scientific American, August 11, 2004; BBC News Online, August 11, 2004; Journal of Optics A: Pure and Applied Optics, Volume 6, Number 9, September 2004, Pages 869-874