In the image recognition processing, input color image data is analyzed, and a specific pattern contained in the graphics of the bill, security or the like is detected. The color image data is binarized with regard to specific colors. In order to detect the specific pattern from the binary image, a filter is sequentially moved to scan the entirety of the binarized image data. The examination target image within the filter is subjected to linear conversion (without changing the size thereof) at each examination position, and the degree of correlation between the pre-linear conversion image and the post-linear conversion image are calculated. It is then determined based on the calculated degree of similarity (i.e., the degree of matching) whether or not the specific pattern is included in the examination target image.