A technology that enables accurate position specification on an image displayed on a screen to perform processing and correction of the image data is provided. When the image is printed on a sheet on which a dot pattern is printed, a reference point of the image on the display device is set and the reference point is printed in a visible mark together with the image. This mark is imaged with an imaging means, and calibration is performed in which position coordinates of the marks on the sheet and the reference points of the image are matched, thereby preventing variation in coordinates between designation made on the sheet with the imaging means and processing on the image.