1. An image processing method for judging whether an obtained document image is similar to a preliminary reference image and then, on the basis of the judgment result, performing image processing on the document image, comprising: a step of storing a plurality of type identifiers each of which contains one or a plurality of image identifiers each for identifying each of a plurality of reference images and thereby identifies a type of a document; a judgment step of judging whether the obtained document image is similar to a reference image; a selection step of, when the document image is judged as being similar to a reference image in said judgment step, selecting an image identifier which identifies the reference image from among the stored image identifiers; and a determination step of, for each type identifier which contains the image identifier selected in said selection step, determining whether the image identifier contained in the type identifier corresponds with the image identifier which identifies the reference image judged as being similar to the document image.