Device for transfer of secret information, e.g. a PIN code for use with a bank or credit card, has interfering line patterns on a transparent film that are covered by blackened section

摘要

Device for transfer of initially secret information according to the method described in in which a sheet is provided with a stamped section over which an essentially transparent film is overlaid with a line pattern on it. The inventive device has a further line structure, necessary for decoding the information, attached to the rear side of the film, while the stamped section has a black color surface on its side adjacent to the film. To visualize the secret information the black color surface is removed revealing the interference between the two line structures that defines the secret code.