Unique “fingerprints” of banknotes could be used to spot counterfeits


Although a growing number of countries are turning to stronger, more difficult-to-copy polymer banknotes, things remain are being counterfeit. New technology could help eliminate these fakes by taking their fingerprints.

During the manufacture of polymer banknotes, the application of a so-called opacity layer leaves a random dispersion of impurities in the ink. The resulting dirt pattern is unique to each individual banknote and cannot be duplicated, but it can be imaged by illuminating the translucent banknote from behind.

Using a commercially available film negative scanner, scientists at the University of Warwick were able to capture these patterns – or “fingerprints” – from a specific small area out of a total. of 340 British banknotes. These images were converted into vector image files, which could then be matched back fingerprints on the original notes, when they have been re-scanned in that same area.

A £ 10 banknote is scanned

University of Warwick

The idea is that if a banknote were suspected to be a fake, it could be scanned for its fingerprint. If that fingerprint did not match the one in an official government database, for the genuine note with the same serial number, then authorities would know that the suspicious note was indeed a counterfeit.

And as a bonus, a veneer finish that is already applied to the banknotes has been shown to protect the fingerprint patterns from rough everyday handling.

That being said, if every banknote in circulation had its fingerprint in a database, wouldn’t that be an unmanageable amount of data to store and process?

“If we take the UK as an example, there are currently almost 4 billion banknotes in the country,” Professor Feng Hao of Warwick tells us. “For each post, the footprint is approximately 2,048 bits, or 256 bytes. The total footprint size for 4 billion banknotes is 1024 GB. In practice, this technique can only be applied to high value banknotes, eg £ 50. The £ 50 banknote amount is around 351million, so you only need a little over 100gb. The number of banknotes in the US will be more, but the data size is certainly manageable. .

The technology, called Polymer Substrate Fingerprinting, is described in a recently published article in the journal IEEE Xplore.

Source: University of Warwick

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