The best-known banknote copy protection feature is the so-called EURion constellation, used by more than 50 countries – including the UK -- and all Euro region notes. It’s a discrete pattern of dots or rings, usually coloured yellow, orange or green, in the shape of Orion star formation. They can be disguised as musical notes or made very small and repeated (as on the £10 note). Software in colour copiers and some PC image editing and scanning programs (Adobe PhotoShop, PaintShop Pro etc.), recognise the pattern and display the message you’ve been seeing. The other, less well-known but possibly more widely used method is the Counterfeit Deterrence System (CDS). This is an algorithm developed for the Central Bank Counterfeit Deterrence Group (CBCDG – part of the G11 group of countries) and is incorporated into the operating system of printers, scanners and copiers and PC scanning applications. For obvious reasons it’s precise mode of operation is a closely guarded secret but basically it looks for specific patterns in the fine lines that make up the design in most banknotes, which are replicated even in small areas of the note.