Recent advances in coherent and incoherent optical information processing systems have brought into use communication and information theory to analyze their performance. An optical information processing system can be analyzed with many of the same concepts of linear system theory (e.g., spatial impulse response, spatial frequency and spatial domain synthesis, etc.), and the photographic images to be processed can be regarded in the same manner as time signals (e.g., spatial frequency content, spatial amplitude and phase modulation, space-bandwidth product, etc.). Both coherent and incoherent optical processing systems can be treated as linear systems and the processing operations can generally be carried out by communication theory concepts. Although coherent optical information procesing operations have been used for performing complex amplitude operations, complex processing can also be performed with partially coherent or even white-light illumination. The importance of optical information processing operations, either coherent or incoherent, is due to the basic Fourier transform property of lenses. In this paper, we will discuss mostly the partially coherent systems because they are of more recent interest and possess certain advantages, we feel, over the traditional coherent optical processors. Experimental illustrations of the results are provided. In view of the broad area of optical image processing, we will confine ourselves to a few applications that we consider of general interest.