Researchers at the University of Warwick, and their collaborator at Durham University, have developed a technique that identifies every banknote’s fingerprint, which is unique and unclonable.

Since plastic (polymer) banknotes were introduced 2016, the number of counterfeit notes on the streets has increased. This new technique could help prevent the rising trend of counterfeit banknotes.

Even though it’s popular to pay with cards and contactless payments today, banknotes still play an important role in our society. Worldwide there are 500 billion banknotes in circulation, making counterfeit notes a great threat to both our society and our economy.

Scientific discovery of banknote “fingerprints”

The researchers at the University of Warwick and Durham University discovered that every polymer banknote has a unique “fingerprint” caused by the inevitable imperfection in the physical manufacturing process, whereby the opacity coating (a critical step during the production of polymer note) leaves an uneven coating with a random dispersion of impurities in the ink. This imperfection results in random translucent patterns when a polymer banknote is backlit by a light source.

Invention of the “fingerprint” testing procedure

The research team has presented a low-cost procedure to identify and capture these unique patterns in banknotes by using a negative-film scanner, and processing them into a compact, 2048-bit feature vector (fingerprint).

The image analysis focuses on a small feature area, where the random translucent patterns from the opacity coating layer are directly exposed without being obstructed by security printing. For the example of the £10, the chosen feature lies between the “ten” hologram and the see-through window. The random patterns extracted from the opacity coating layer form the unique “fingerprint,” which is further protected by a veneer finish applied on both sides of the polymer note, making it robust against rough handling in daily use.

Using 340 banknotes, the researchers collected a large-scale dataset of 6,200 sample images and have proved that their technique can identify each banknote’s fingerprint successfully, despite rough daily handling.

Confounding the Counterfeiters

Professor Feng Hao, of the University of Warwick’s Department of Computer Science, summed up the discovery and corresponding testing technique: “Like every human has unique biometric features, we have found every polymer banknote has its own ‘bio-metric’, which is unique, naturally occurring, and can’t be physically cloned. This new finding gives us the basis to design a completely new anti-counterfeiting method for banknotes. “Something universally believed is that once counterfeiters have access to essentially the same printing equipment and ink as used by legitimate government to print fake banknotes,

the game is over, as there will be no way to distinguish genuine and fake banknotes. Contrary to this belief, our research shows, perhaps surprisingly, that there is still hope to defeat counterfeiting even in that extreme scenario.”


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