Although an increasing number of countries are switching to sturdier, harder-to-copy polymer banknotes, the things still are being counterfeited. A new technology could help weed those fakes out, by taking their fingerprints.
During the production of polymer banknotes, the application of a layer known as the opacity coating leaves a random dispersion of impurities in the ink. The resulting pattern of impurities is unique to each individual banknote, and cannot be duplicated, but it can be imaged by illuminating the translucent note from behind.
Utilizing a commercially available film negative scanner, scientists from the University of Warwick were able to capture those patterns – or "fingerprints" – from a specific small area on a total of 340 British banknotes. Those images were converted to vector image files, which could subsequently be matched back to the fingerprints on the original notes, when they were rescanned in that same area.
The idea is that if a banknote were suspected of being a fake, it could be scanned to obtain its fingerprint. If that fingerprint didn't match the one which was in an official government database, for the genuine note with the same serial number, then the authorities would know that the suspected note was indeed a counterfeit.
And as an added bonus, a veneer finish which is already applied to the notes has been shown to protect the fingerprint patterns from daily rough handling.
All 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, currently there are nearly 4 billion notes in the country," Warwick's Prof. Feng Hao tells us. "For each note, the fingerprint is about 2,048 bits, so 256 bytes. The total size of the fingerprints for 4 billion notes is 1,024 GB. In practice, this technique may be applied to high-value notes only, e.g., £50. The amount of £50 notes is about 351 million, hence you only need just over 100 GB. The number of banknotes in the US will be larger, but the size of the data is certainly manageable."
The technology, which is called Polymer Substrate Fingerprinting, is described in a paper that was recently published in the journal IEEE Xplore.
Source: University of Warwick