Image processing apparatus, pattern detecting method, and recording medium

An image processing apparatus is provided that can make judgment of a specific pattern accurate and easy and can judge a copying-prohibited original document regardless of the color of the original document and inputted image information of the copying-prohibited original document added with the specific pattern and even when the size of the specific pattern differs. A black detecting color filter executes a binarizing process to inputted image data in terms of black, and a yellow detecting color filter executes a binarizing process to inputted image data in terms of yellow. The black and yellow primitive pattern detecting portions respectively detect black primitive patterns and yellow primitive patterns from the black and yellow binarized image data. The copying-prohibiting added pattern detecting portion detects a specific pattern based on an arrangement of the primitive patterns detected by the black and yellow primitive pattern detecting portions.