In a card serving as an external storage device to be inserted into a digital color multi-function printer, features of a reference image and processing rule information indicating processing content to be applied to input image data judged to be similar to the reference image are prestored. Then, in cases where the input image data is judged to be similar to the reference image, the content of a process to be performed on the input image data is controlled in accordance with the processing rule information corresponding to the reference image. This makes it possible to save users the trouble of setting the content of a process to be performed on input image data, and to prevent a shortage of memory capacity of a memory of the image processing apparatus even in cases where there is an increase in the number of reference images.