In dynamic scenes, the presence of object boundaries is often signaled by the appearance or disappearance of occluded surfaces over time. Such regions of surface accretion or deletion can be found using matching techniques similar to those used to determine optical flow in an image sequence. Regions in one frame that are not adequately matched by any region in previous frames correspond to accretion. Regions that have no matches in subsequent frames correspond to deletion. In either case, an occlusion boundary is present. Furthermore, by associating accretion or deletion regions with a surface on one side of a boundary, it is possible to determine which side of the boundary is being occluded. This association can be based purely on visual motion-the accretion or deletion region moves with the same image velocity as the remaining visible surface to which it is attached.