The Secret Dots That Stop Photocopiers
Look closely at many modern banknotes, and you might spot a pattern of five tiny, colored circles. This is the EURion constellation. Most color photocopiers, scanners, and image-editing programs are hardcoded to detect this specific geometric arrangement. If they find it, they instantly refuse to copy or print the document, preventing casual counterfeiters from duplicating cash at home.
The Geometry Hidden in Plain Sight
On the surface of many contemporary banknotes circulating across the world, a careful observer can find an unobtrusive repeating pattern of tiny rings. These circles, often printed in faint shades of yellow, green, or orange, measure less than a millimeter across. Rather than standing out as security seals or high-contrast badges, they are woven seamlessly into the background artwork, masquerading as musical notes, constellations, background textures, or the zeroes in printed numbers.
Despite their subtle appearance, these rings serve as a worldwide digital tripwire. When modern color photocopiers, desktop scanners, and multifunction office printers scan an item containing this specific geometric arrangement, internal firmware recognizes the layout and abruptly halts the operation. The machine may shut down the print job entirely, spit out an error page, or print a solid black band over the document, thwarting attempts to reproduce currency with consumer-grade hardware.
Markus Kuhn and the 2002 Discovery
For years, the mechanism that caused office copiers to reject currency went unacknowledged in public documentation. The arrangement came to broader public attention in 2002 through the work of Markus Kuhn, a computer science researcher at the University of Cambridge. While experimenting with a Xerox color photocopier that persistently refused to copy a newly issued ten-euro banknote, Kuhn decided to isolate the visual elements on the bill to see what triggered the hardware lock.
By methodically covering different portions of the banknote and attempting to copy it, Kuhn narrowed down the trigger to a small, recurrent cluster of five circles. Recognizing that the spatial layout resembled the constellation Orion, Kuhn coined the term EURion constellation—combining EUR, the international currency code for the euro, with the name of the celestial constellation. Kuhn published his findings online, demystifying the covert standard that central banks and printer manufacturers had quietly integrated across hardware pipelines.