Optical pattern recognition and in particularly optical correlation has been the subject of intensive research for many years. The basic principle consists of the comparison of a reference image with the scene to analyze. The potential advantage of optical technologies is their ability to determine the conelation function very rapidly. Most of the research effort has concentrated on technology, and particularly on the spatial light modulators (SLM) which enable to encode the reference and the input images on a coherent optical beam and on the detectors. The recent availability of efficient SLM's and fast detectors has allowed the realization of different [1,2,3] optical correlator demonstrators and the question of their practical fields of applications becomes more stringent.