A system and method processes intensity images having a ring structure to measure position, shape deviation and/or radius of the ring structure, and to evaluate interferograms and/or localize objects. The system and method can define N sectors of the intensity image respectively having sector tips lying at a common sector origin within the ring structure, with N being a natural number where N>1, detect a distance of an intensity extreme from the respective sector tip of each sector of at least one group of the sectors to obtain a distance vector that includes the distances from all the sectors from at least the group of the sectors, perform a Fourier transformation of the distance vector, and determine a center, a radius and/or a deviation of the ring structure from a circular shape,-by using the first Fourier vector obtained by the Fourier transformation.