The EURion constellation (also known as Omron rings or doughnuts) is a pattern of symbols incorporated into a number of banknote designs worldwide since about 1996. It is added to help imaging software detect the presence of a banknote in a digital image. Such software can then block the user from reproducing banknotes to prevent counterfeiting using colour photocopiers. Research shows that the EURion constellation is used for colour photocopiers but probably not used in computer software. It has been reported that Adobe Photoshop will not allow editing of an image of a banknote, but this is believed to be due to a different, unknown digital watermark rather than the EURion constellation.
EURion constellation Wikipedia
The name "EURion constellation" was coined by Markus Kuhn, who uncovered the pattern in early 2002 while experimenting with a Xerox colour photocopier that refused to reproduce banknotes. The word is a combination of EUR, the euro's ISO 4217 designation, and Orion, a constellation of similar shape.
The EURion constellation first described by Kuhn consists of a pattern of five small yellow, green or orange circles, which is repeated across areas of the banknote at different orientations. The mere presence of five of these circles on a page is sufficient for some colour photocopiers to refuse processing.
The EURion constellation is most prominent, and was therefore first recognised, on the 10 Euro (€10) banknote.
Some banks integrate the constellation tightly with the remaining design of the note. On 50 DM German banknotes, the EURion circles formed the innermost circles in a background pattern of fine concentric circles. On the front of former Bank of England Elgar £20 notes, they appear as green heads of musical notes, however on the Smith £20 notes of 2007 the circles merely cluster around the "£20" text. On some U.S. bills, they appear as the digit zero in small, yellow numbers matching the value of the note. On Japanese Yen, these circles sometimes appear as flowers.
Technical details regarding the EURion constellation are kept secret by its inventors and users. A patent application suggests that the pattern and detection algorithm were designed at Omron Corporation, a Japanese electronics company. It is also not clear whether the feature has any official name. The term "Omron anti-photocopying feature" appeared in an August 2005 press release by the Reserve Bank of India. In 2007 it was picked up in an award announcement by a banknote collectors society.
The following table lists the banknotes on which the EURion constellation has been found so far. Countries where all recent banknotes use the constellation are in bold.
Recent versions of image editors such as Adobe Photoshop or Paint Shop Pro refuse to print banknotes. According to Wired.com, the banknote detection code in these applications, called the Counterfeit Deterrence System (CDS), was designed by the Central Bank Counterfeit Deterrence Group and supplied to companies such as Adobe as a binary module. However, experiments by Steven J. Murdoch and others showed that this banknote detection code does not rely on the EURion pattern. It instead detects a digital watermark embedded in the images, developed by Digimarc.