Image understanding requires mutual interaction of processing steps.
A human being is well prepared to do image processing, analysis and understanding. Despite this fact, it may sometimes be difficult to recognize what is seen if what to expect is not known. The main difference between a human observer and an artificial vision system is in a lack of widely applicable, general, and modifiable knowledge of the real world in the latter. Machine vision systems construct internal models of the processed scene, verify them, and update them, and an appropriate sequence of processing steps must be performed to fulfill the given task. If the internal model matches the reality, image understanding is achieved.