An image data identifying unit identifies at least two pieces of image data for images displayed in display regions detected by a detecting unit. The at least two pieces of image data includes a first image data firstly identified by the image data identifying unit. An image data selecting unit selects or deselects the at least two pieces of image data identified by the image data identifying unit. A selection data storing unit stores selection data for each of the plurality of pieces of image data read by a reading unit. The selection data indicates whether each of the plurality of pieces of image data is in a selected state or a deselected state by the image data selecting unit. A determining unit determines whether the first image data is in the selected state or the deselected state based on the selection data. The image data selecting unit sets the at least two image data to the selected state when the determining unit determines that the first image data is in the deselected state, and sets the at least two image data to the deselected state when the determining unit determines that the first image data is in the selected state.