Nonlinear optical systems are presented, giving possibility to change complex light fields characteristics with the aim of image processing on the base of nonlinear optical effects, such as stimulated scatterings of light, two-photon excited luminescence, Kerr-effect etc. These systems allow to perform image processing, changing characteristics of the complex light field, forming the image. For instance, we can change image contrast from that of initial image to the contrast inversion. It's possible also to visualize phase and low-absorbing objects, phase inhomogeneities in transparent materials, thickness variations of low-absorbing layers and roughness of reflecting surfaces. Thus, these methods can find wide applications in materials technologies monitoring, biology and medicine. Image processing is performed in real-time scale, which permits to avoid influence of effects, connected with light beam propagating in materials, and to study quick processes.