The name "EURion constellation" was coined by Markus Kuhn, who discovered the pattern in early 2002 while experimenting with a Xerox colour photocopier that refuses to reproduce banknotes. The word is a portmanteau of Orion, a constellation of similar shape, and EUR, the euro's ISO 4217 designation.

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. Andrew Steer later noted simple integer ratios between the squared distances of nearby circles, which gives further clues as to how the pattern is meant to be detected efficiently by image-processing software.

The EURion constellation is most prominent and was therefore first recognised on the 10 Euro banknote.

Some banks integrate the constellation tightly with the remaining design of the note. On German banknotes, the EURion circles formed the innermost circles in a background pattern of fine concentric circles. On the front of English £20 notes, they appear as green heads of musical notes. On U.S. dollar bills, they form the digit zero in little yellow numbers that show the value of the note.

Technical details regarding the EURion constellation remain kept secret by its inventors and users. A patent application suggests that the pattern and detection algorithm were designed at OMRON Corporation.

Users of recent versions of image editors, such as Adobe Photoshop or Paint Shop Pro, discovered that these also refuse to print banknotes. According to an article in Wired magazine, 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 detects other features of banknote designs that have yet to be described in public.