The EURion constellation is a pattern made up of five rings that are added to banknotes in order to prevent counterfeiters from creating forgeries using colour photocopies. Though the pattern has been used on banknotes around the world for nearly 15 years, the name was coined in early 2002 by a German computer scientist named Markus Kuhn who uncovered the pattern while experimenting with a Xerox colour photocopier that refused to reproduce banknotes.
Combing the words “Orion” and “Euro,” the EURion constellation can be found at various locations on banknotes – depending on the design – and is used on currency across the globe.
Many banks and banknote producers integrate the EURion constellation into the design of bill in order to mask its presence. On a 50DM German banknote, for example, the EURion constellation forms tiny circles in a background pattern hidden amongst other circles. On the former Bank of England £20 Elgar notes, the constellation appeared as green heads of musical notes. On some US bills, they appear as a zero in small, yellow numbers matching the value of the note.
The technical details of the EURion constellation are highly secretive. Some have speculated that the integer ratios between the squared distances of nearby circles are what cause software to recognize that the banknote is trying to be copied. Much like the software employed by the Central Bank Counterfeit Deterrence Group, the EURion constellation tips off the copying device and prevents forgeries.
Some scientists, however, have hypothesized that the EURion constellation isn’t the device triggering the software. Steven Murdoch, a security researcher at the University of Cambridge Computer Laboratory, has said he believes the trigger is instead a digital watermark embedded in the notes.
Currently, over 40 countries use the EURion constellation on their banknotes including the United States, Canada, Turkey, Sweden, India, Norway, and Australia.