a technique for correlating two images , differing in size , but of identical spatial content . the technique is based on the cauchy - schwarz inequality and is derived in such a way as to eliminate the requirement for division , thereby realizing practical real time implementation with presently available electronic hardware . in the embodiment disclosed , reference and data image signals require no pre - processing for the removal of mean and gain factors prior to being individually supplied to the correlator . the correlator is built around modules which can be configured serially with delay lines to adapt to virtually any image configuration . simulation tests have shown the embodiment to be superior to prior art correlators utilizing other algorithms under conditions of noise , offset and gain differences .