The invention is provided with: an acquisition unit that acquires, from an external machine, image data as well as time data when an image based on the image data has been displayed on the external machine; a data memory unit that stores, for each unit of the image data, the image data and the time data acquired in the acquisition unit; and a prioritization determination unit that determines, on the basis of the time data, a prioritization of the image data stored in the data memory unit.