1. A computer-implemented method for allocating retrieval keys to frame intervals that form portions of an entire sequence of frames that constitute a stored motion image and updating an index file of motion image frame intervals on a storage medium, said index file comprising records that contain information on initial and final positions of said intervals in said motion image as well as information on said retrieval keys, said method comprising the steps of: a. receiving as input a designation of one of said retrieval keys as a currently designated retrieval key; b. receiving as input a designation of initial and final positions of one of said intervals; c. extracting, from said index file, records that contain information on said currently designated retrieval key, in response to the designation of said initial and final positions; d. checking for the existence of any overlaps between said initial and final positions of said designated interval and the intervals defined by said extracted records; e. if any overlaps are detected in step (d), updating said index file so that it does not include any records associated with intervals that cause an overlap, but includes a record that contains information indicating initial and final positions of an interval that includes all the intervals that cause the overlaps, as well as information on the currently designated retrieval key; f. if no overlaps are detected in step (d), inserting into said index file a record that contains information on said designated initial and final positions as well as on said currently designated retrieval key; and g. iterating steps (b) through (f) until the designation of a new retrieval key is received as input.