METHOD AND APPARATUS FOR DETECTION OF DOCUMENT TAMPERING

The invention relates to a computer-implemented method, and apparatus, of testing a digital image (10a, 10b) of a cheque (check) or other document for indications that it was subject to tampering. The digital image comprises a set of pixels each having one or more pixel values. The method comprises analysing the digital image to identify contiguous sets of pixels over a predetermined size in which all the pixels in a set have pixel values which match those of the other pixels in the set to within a predetermined margin. The identification of image regions may comprise testing pixels within a cell and counting the number of pixels whose pixel values match a reference pixel. Further disclosed is a computer-implemented method and apparatus for testing a document for features suggestive of tampering which includes the identification of marked pixels, defining a set of tiles, calculating, for each of the tiles, a tile image density and analysing tile image densities to determine whether any is suggestive of tampering. The inventions may have particular use in electronic cheque clearing systems and allow the detection of washing, coating or other alteration of the cheque or document which results in a background pattern being removed.