Patent ID: 7035428

Claim:
An indicium for placement on a workpiece for use in determining whether the workpiece is valid, comprising: a set of one or more markings corresponding to a string that is based upon, at least in part, intrinsic physical characteristics of at least one portion of said workpiece, said physical characteristics including one or more images of surface topographical appearance of said at least one portion of said workpiece resulting when the at least one portion of said workpiece is illuminated with electromagnetic radiation from different illumination positions relative to said at least one portion, the string being further based upon, at least in part, a numerical hash value derived from the one or more images, the value being generated by a process that includes extracting from the one or more images a first image portion scaling the first image portion to generate a scaled image portion, averaging pixel value of the scaled image portion to generate a first filtered image, extracting from the first filtered image a second image portion, averaging pixel values of the second image portion to generate a second filtered image, and subtracting corresponding pixel value of the second filtered image form the second image portion to generate a third filtered image.