Cine film and videotape are used to record a variety of natural processes in biology, medicine, meteorology, etc. This paper describes a system which detects and tracks moving objects from these records to obtain meaningful measures of their movements, such as linear and angular velocities. Features of the system are as follows. 1) In order to detect moving objects that are usually blurred, temporal differences of gray values (differences between consecutive frames) are used to separate moving objects from stationary objects, in addition to spatial differences of gray values. 2) The results of previous frames are used to guide feature extraction process of the next frame so that efficient processing of moving pictures which consists of a large number of frames is possible. 3) Uncertain parts in the current frame, such as occluded objects, are deduced using information of previous frames. 4) Misinterpreted or unknown parts in previous frames are reanalyzed using the results of later frames where those parts could be found.