Image Processing is a typical domain where one has to implement knowledge-based systems integrating cooperative activities, on the one hand between human experts, when knowledge acquisition is concerned, and on the other hand between human experts and system, when problem-solving is concerned. Designing Image Processing applications involves three types of expertise: expertise about the domain of application, where the application is specified, Image Processing expertise, where a solution in terms of Image Processing operations is proposed, and expertise about computer design concerned with finding a satisfactory implementation of the system. In this article, cooperative processes are presented along two aspects: knowledge acquisition and problem-solving. In the first case, the user directs the resolution stage, whereas the system provides him with its abilities in ergonomics, computation or storage. In the second case, it is the system that solves problems, and the experts can intervene either when they are questioned by the system to get additional information about the problem, or spontaneously to modify choices made by the system or correct some of its deficiencies.