Patent US 5,790,932

An image forming apparatus, such as a copying machine, is provided with a function of detecting in an original presented for copying, a particular image which should not be copied, for example, banknotes and other negotiable instruments. Upon detection of such image in an original presented for copying, the apparatus, in reproducing the image, synthesizes with that image a pattern denoting information which identifies the particular machine on which the copying was performed. For example, the pattern used for that purpose may be the manufacturer's serial number. In particular, the machine may binary-code input image data before synthesis with the pattern. According to another aspect, the apparatus and method of the invention discriminate the degree of similarity between input image data and the predetermined image which is not to be copied, delays the input image data during performance of the discrimination, and processes the delayed image data in a way which depends upon the degree of similarity discriminated. The discrimination of similarity may be based on the color distribution in the input image data. The structure for actually reproducing the image, whether synthesized with the serial number or not, may preferably be a bubble jet printer.