The segmentation of deformable structures is an important task of image analysis. Satellite image sequences provide a huge amount of data often displaying the temporal evolution of complex structures, like clouds in the atmosphere on meteorological data. Structures like clouds and vortices are also subject of fusions, or can dissolve themselves into many connected components. Powerful deformable models, like the level-sets methods, are steadily gaining ground in image analysis and computer vision. In the research conducted in the AIR project at INRIA-Rocquencourt, a new characterization of level-sets by particle systems is achieved, leading to models that can be interactively controlled by an operator and permit the modeling of complex visco-elastic structures in motion. The control of level-sets by particle systems gives the possibility of using fast numerical resolution algorithms. It also features the attractive property of assigning specific internal or external energies to the level-sets, simply by prescribing particular forces on the finite set of particles. It also gives the possibility of analyzing motion.