An object of the present invention is to provide an image processing apparatus which allows a user to execute image processing, such as extraction and elimination of a portion common to a plurality of images therefrom, with a simple operation. An image of a document is read by a scanner, and when the document is a first one, the image of the document is stored from input means into storing means. When an image of a second document is read, comparing means compares the read image with the image stored in the storing means to judge whether or not a difference in pixel values between the first document image and the second document image is smaller than a threshold value set through setting means. A portion in which the difference in pixel values is judged smaller than the threshold value is recognized as a common portion, and in accordance with a result of selection by selecting means, the portion is sent as a result of extracting the portion common to the plurality of inputted images therefrom, to an image processing section via output means and printed by a printing mechanism, or the respective images from which the common portion is eliminated are sent from the output means to the image processing section and outputted by the printing mechanism.