The present invention provides an image processing apparatus including: an image reading section for reading a document image; a particular image determining section for determining whether or not a particular image is included in image data read by the image reading section; an image processing section for processing the image data; and a resolution converting section for changing a resolution of the image data to be transferred to the particular image determining section, wherein the resolution converting section lowers a pixel frequency of the image data to be transmitted to the particular image determining section so as to perform simple processing. The lowered pixel frequency slows down processing speed of the image data and thereby improves determination accuracy.