TWI680668B

A method includes: a full-screen image acquiring step in which full-screen image data displayed on a screen of a display is sequentially acquired; a compressed full-screen image creating step in which a full-screen image acquired in the full-screen image acquiring step is compressed every predetermined recording time period to create a compressed full-screen image; a splitting step in which the full-screen image data acquired in the full-screen image acquiring step is split into block images in a predetermined size from one end of a screen area; a positional information creating step in which block images at two sequential time instants are compared in every block image split in the splitting step to create positional information data expressing presence or absence of a difference and positional information about a block considered to have a difference; and a compressed difference image creating step in which a block determined as a block considered to have a difference in the positional information creating