1. An image-comparing apparatus for comparing a code stream obtained by encoding a retrieved image, with a specific image, thereby to determine whether the code stream is substantially identical to the specific image, the apparatus comprising: image-characteristic amount extracting means for analyzing the code stream, thereby to extract an image-characteristic amount of the retrieved image; encoding-parameter extracting means for extracting an encoding parameter from the code stream; encoded-data generating means for encoding the specific image to some extent, on the basis of the encoding parameter, thereby to generate encoded specific-image data; and comparing means for comparing the image-characteristic amount of the retrieved image with the encoded specific-image data, thereby to determine whether the code stream is substantially identical to the specific image.