A situated approach to Markovian image segmentation is proposed based on a distributed, decentralized and cooperative strategy for model estimation. According to this approach, the EM-based model estimation is performed locally to cope with spatially varying intensity distributions, as well as non-homogeneities in the appearance of objects. This distributed segmentation is performed under a collaborative and decentralized strategy, to ensure the consistency of segmentation over neighboring zones, and the robustness of model estimation in front of small samples. Specific coordination mechanisms are required to guarantee the proper management of the corresponding processing, which are implemented