An image is digitally watermarked to convey position data about the subject of the image, such as latitude, longitude and elevation of a point depicted therein. According to the invention, two or more kinds of spacers which differ in height from a reference surface are disposed on one of the pair of substrates. And the interoperability between color features quantized into different quantization levels is provided so as to search multimedia generated from different application programs and in which a quantization rule is defined so as to maintain high search performance. If it is not, one or more other areas in the image are selected andor the size, shape, aspect ratio of the overlay element is changed until a position andor size, shape, aspect ratio is found which minimizes occlusion of the desirable viewing areas in the image.