A method, apparatus, and program for image processing are provided to perform operations of generating a verification document image and detecting tampering on the verification document image. The verification document image is generated by a document image generator, which adds a verification pattern to an original document image received from a document provider. A tampering detector determines whether the verification document image has been tampered based on the verification pattern. The output unit prints out, under control of a controller, the verification document image as well as information on whether tampering is detected. The above operations are performed on a network, such as the Internet.