1. A computer-implemented process for generating a representation of an object, comprising using a computer to perform the following process actions: for a prescribed number of directions, determining the thickness of the object along each of a prescribed number of parallel rays directed through the object in the direction under consideration, normalizing the determined thickness values, and generating a thickness histogram from the normalized values; wherein the thickness histograms associated with the prescribed directions define a directional histogram model of the object which is employed as a representation of the object that is substantially invariant in regard to translation and scaling.