Abstract: A processing unit (workstation) is connected through a communication line to an image managing unit (server) to manage a data base in which real image data has been stored. A teaching data forming section of the processing unit forms mask teaching data indicative of an object outline with respect to thin-out image data obtained from the real image data stored in the data base as a target and transfers to the image managing unit as a server. A mask data forming section of the image managing section forms mask data indicative of the object outline from the real image data in the data base by using the transferred mask teaching data as a reference (guidance).