Method and system for estimating the robustness of algorithms for generating characterizing information descriptive of a selected text block

A method and system for selecting a characterising algorithm to be used to characterize blocks of printed material. A digital image of printed material, such as an address block, on an object is obtained, and the image is processed to abstract characterizing information descriptive aspects of the other printed material. The characterizing information is combined with other information, such as postal information, and the combined information is then cryptographically authenticated with a digital signature or the like, An indicium representative of the authenticated information is then printed on the object. The object's relationship to the indicium can be verified by regenerating the characterizing information from the other printed material and comparing the regenerated characterizing information with characterizing information recovered from the indicium. Thus copies of the indicium cannot easily be used, without detection, on other objects which do not include the other printed material, A particular algorithm is selected from a predetermined group of characterizing algorithms by determining an estimate for the robustness of each algorithm with respect to small changes in the image caused by the printing and scanning process or by defacing of the printed address by blots or the like.