EURion constellation

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 . 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.

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 2002 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.

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