1. An image recognition method in which a mask pattern indicating characteristics of image patterns to be recognized is used to recognize the image patterns from target image data having digitized gradations of two or more values, comprising: said mask pattern having a first pattern area and a second pattern area; obtaining a first representative value which is a luminance of the target image data from the first pattern area; obtaining a second representative value which is a luminance of the target image data from the second pattern area; and judging that an image to be recognized is present in the target image when a result of comparison between the first and the second representative values satisfies a predetermined condition.