Nowadays, motion estimation is one of the main subjects in computer vision. Many methods developed to compute motion make use of the optical flow hypothesis. These methods usually fail to capture motion of objects with intensity evolution. We propose a new approach to solve the motion computation problem with a different type of constancy hypothesis. Because we are mainly interested in deformable moving structures, we postulate that such a structure, within a temporal image sequence, is associated with a constant volume or a constant total intensity over time. We call this postulate it the volume conservation hypothesis. Results are displayed for clouds motion and deformation on meteorological satellites images.