1. An image comparing apparatus for comparing a code stream obtained by coding an image with a specific image to decide whether to match, comprising: a vector calculating unit for calculating a first vector indicative of a correlation between the number of zero bit planes of a code block of interest to be processed and the number of zero bit planes of a code block near the code block of interest based on the number of zero bit planes of the code stream; a vector output unit for outputting a second vector indicative of a correlation between the number of zero bit planes of a code block of interest in the specific image and the number of zero bit planes of a code block near the code block of interest; and a comparing unit for sequentially comparing a first vector from the vector calculating unit with a second vector from the vector output unit for code blocks of interest at the same position of the code stream and the specific image and deciding whether the code stream matches with the specific image depending on a comparison result.