A predetermined position on a paper sheet is pointed by a finger, and a first image of the paper sheet picked up by an image pickup device before pointing by the finger is stored. A second image of the paper sheet picked up by the image pickup device upon pointing by the finger is stored. By subtracting...http://www.google.com.hk/patents/US5687333?utm_source=gb-gplus-share專利 US5687333 - Information service system responsive to user's pointing manipulation
