1. A method for identifying an object image that uses a density difference between a background image and an object image in a picture, said method comprising the steps of: arranging a Standard Object image on a picture in which an arrangement point, which is an arbitrary point on said picture that shows a background image, is used as a reference point; determining a normal vector group on outline portions of said Standard Object image based upon density difference in said background image and said Standard Object image; determining an angle information of respective normal vectors and determining a position information from said arrangement point to said respective normal vectors of said normal vector group; storing said position information and angle information as standard data for said arrangement point; determining, for a picture that shows an object image to be recognized, a normal vector group on outline portions of said object image based upon density difference in said object image and a background image; determining a plurality of Answer point groups, that correspond to said arrangement points, from said normal vector group based upon said standard data; and evaluating a focus point region formed by said Answer point group.