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 device 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 device 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, wherein the vector output device outputs the second vector calculated based on the number of zero bit planes for each code block obtained when coding the specific image using coding parameters not containing a quantization step size among the coding parameters used when coding the code stream; and a comparing device sequentially comparing a first vector from the vector calculating device with a second vector from the vector output device 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.