The EURion constellation is a pattern of symbols found on a number of banknote designs since about 1996. It is added to help 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.


Pretty interesting on the mechanism that copy machines use to detect and block the copying of a banknote.

Link:
http://en.wikipedia.org/wiki/EURion_constellation

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