Digital image comparing system

A system (1) for comparing digital images, whereby a first and second data processing block (5, 6) receive respective data streams (I, I') corresponding to a reference image (S) and a detected image (S') for comparison with the reference image (S). The data processing blocks (5, 6) detect reference points in the images, and generate data (P1, P4), which is supplied to a block (10) for determining a first approximation of the function Ao(X,Y,alpha) relating the two images (S, S').The system also presents blocks (17, 27) for successively refining the function relating the reference image (S) to the detected image (S').