EURion constellation: Difference between revisions

Revision as of 07:20, 23 July 2005

Revision as of 01:47, 28 July 2005

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[[Image:10e rec.png|thumb|250px|The small circles or dots constituting the EURion constellation are clearly visible on the centre-left of 10 [[euro]] banknotes.]]

[[Image:EURion20GBP.JPG|thumb|150px|On the Bank of England £20 the EURion constellation appears as "musical notes".]]

A number of recent [[banknote]] designs contain a pattern now known as the '''EURion constellation'''. 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. The name was coined by [[Markus Kuhn]], who discovered it in early [[2002]] while experimenting with a [[Xerox]] colour photocopier that refuses to reproduce banknotes. ItThe word is a [[portmanteau]] of [[Orion (constellation)|Orion]], a [[Constellation|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. 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.