For automatic recognition of the authenticity of items in sheet form such as bank notes, for example in an automatic service machine, the transparency of each bank note is examined in predetermined spectral ranges. The measuring system is arranged between units of a transport system and, in a passage...http://www.google.co.uk/patents/US5034616?utm_source=gb-gplus-sharePatent US5034616 - Device for optically scanning sheet-like documents
