Abstract: A certifier device (90) for producing a certified document (101) of an original document (100) and a verifier device (300) for verifying the certified document (101). The certifier device (90) includes a scanner (102) for scanning the original document (100) to generate a true copy image. The certifier has also an encoder (104) for computing a digital code which is representative of the true copy image; an encryptor (108) for encrypting the digital code according to a private key associated with a certifier identification; and a compositor (107) for compositing an image including the true copy image together with the encrypted digital code and certifier identification. The verifier device (300) includes a scanner (301) for scanning the certified document (101); a decryptor (307) for decrypting the encrypted digital code according to a public key associated with the certifier identification; and a encoder (309) for computing a digital code which is representative of the true copy image.

Abstract: A method of determining an indicator for the presence of an image is disclosed in which the image is comprised of a two dimensional array of pixels. The method finds particular use in the prevention of fraudulent copying of images, such as bank notes using colour laser copiers and printers. The method firstly imposes a grid of cells over a portion of the image. Then a representative value for each of the cells is determined. Next, a measure of the difference between the representative values of adjacent cells of the grid is determined over the whole of the grid. The first three steps are then repeated for substantially all possible positions of the grid of cells to determine a grid position having an overall maximum positional difference. Finally, the grid position and the representative value for each of said cells is used as a representation of the image. The representation can thus comprise a template used in an image detection system.

Abstract: An image detection system is disclosed for the detection of an image in an input pixel stream. An image is input as a input pixel stream and accumulated and converted into cells which are formed into cell data portions from regions of a corresponding image of the input pixel stream. A template storage ROM stores at least one template that comprises a multiplicity of cell data entries derived form an desired image to be detected. A comparator matrix is connected to the cell converter and the template ROM for comparing the cell data portions with a multiplicity of cell data entries to derive a template detection signal when a predetermined number of the cell data portions match with the multiplicity of said cell data entries. The system finds particular use in the prevention of fraudulent copying of images, such as bank notes using colour laser copiers and printers.