An imaging technology having high reproducibility of a document and making image correction possible, without being influenced by a way of placing the document or a position of a camera, and irrespective of paper color and despite of damage of a corner portion. By printing positioning symbols on document paper in advance when the document is photographed by a digital camera or a portable phone with a camera, such as a smart phone, and by processing the image based on these positioning symbols, image processing having high reproducibility of the document and making image correction (keystone correction) possible can be implemented irrespective of paper color and despite damage to a corner portion.