Hardware, Technology Security

Optical mouse sniffs out counterfeit money


The most common and prolific computer device, the lowly mouse, is fighting crime. Suspected counterfeit money is scanned, compared, and identified. An optical mouse sensor compares images of a questionable coin with reference images from a genuine coin using a unique algorithm.

Common side of all two-Euro coins minted after 2007For now, the money being analyzed is a coin, the two Euro [?2], the most valuable and most often counterfeited coin in the European Union. In 2007, fake or counterfeit replicas were prolific. There were 211,100 removed from circulation, making a total value of EUR 422,200 or 631,442 US Dollars.

There are eight denominations of the Euro – 1, 2, 5, 10, 20 and 50 cent, ?1 and ?2. They come in different sizes, weights, materials, color and thickness to help individuals who suffer severe eyesight impairments recognize the coin. The variations should also discourage counterfeiters… but you must build a better mousetrap to catch better mice as comedian George Gobel said. That is what a group of researchers in the Department of Computer Science and Industrial Engineering, University of Lleida, Spain have tried to do.

All Euro coins carry a design by Mr. Luc Luycx of the Royal Belgian Mint of their value and a map of Europe. The opposite side carries a locale-specific representation. The two Euro has a golden colored inner circle composed of three layers of brass, encircled with a silver-colored ring of cupronickel. The multi-colors help deter counterfeiters. The coin is 2.20 mm thick, weighs 8.5 grams and has a 25.75 mm diameter. Its edges vary between countries, many being ribbed with lettering.

Low cost sensors in vending machines measure some physical characteristics of coins such as weight, size, thickness, conductivity, and magnetic or acoustic properties. When these physical properties are very similar, image-based coin recognition can be used. The system must detect coins from non EU countries that are similar in size and weight to the two-Euro coin.

Counterfeit coin detection device.  Photo credit: Tresanchez et al. / SINC

The new vision-based measurement system was explained in a paper published by Marcel Tresanchez, Tomàs Pallejà, Mercè Teixidó and Jordi Palacín. The device consists of a dedicated microprocessor, combined with an optical mouse sensor, including a digital signal processor, a CMOS camera, and a lateral infrared light source that illuminates the coin?s surface casting shadows which help detect small variations in the roughness of the surface. A convex lens captures the reflected light. The mouse sensor compares images at over 6,400 frames per second.

Sectional view - assembly components - ADNS-3088 sensor - Courtesy of Avago
Sectional view gives you a nice look into assembled components – ADNS-3088 sensor. Photo credit: Avago

The acquired image is only 1/14 of the front side of the two Euro coin. Tresanchez says images must be captured in real time, with a minimum resolution of 15×15 pixels, and preferably an LED- or infrared-based sensor, instead of laser technology. The research team used the ADNS-3088 optical mouse sensor from Avago Technologies, previously the semiconductor division of HP?s spinoff, Agilent Technologies. In 2005, Avago became an independent company. They produce analog, mixed-signal and optoelectronic components and subsystems.

Coins, but originally animals, have always been a valuable commodity. Bartering of animals and crops came before tangible money ? coins being the first form of monetary exchange. The world?s first coins were made in Lydia and Ionia, now western Turkey, out of electrum, a naturally occurring alloy of gold and silver. Ancienthistory.com defines them as "the world’s first true coins because they were composed of a scarce metal, of a consistent weight, and guaranteed by a government." And we all know, you don?t mess with the government.

Ever since exchanges of value-for-value have existed, some folks have sought a shortcut to wealth, be it counterfeiting or theft. Just as horse thieves faced the hanging rope in the "Old West", in many earlier cultures, coin counterfeiters faced a death sentence. Something to keep in mind. Older mores seem to be coming back in fashion.