1. An image display device, comprising: at least one processor; a display; and at least one memory device that stores a plurality of instructions, which when executed by the at least one processor, causes the at least one processor to execute operations comprising: generating a plurality of image sets, each including a plurality of modified images that are obtained by modifying an original image, wherein an average of pixel values of corresponding pixels of the plurality of modified images included in each of the image sets corresponds to a value of a corresponding pixel of the original image, and numbers of the modified images included in each of the image sets are different from each other; and sequentially using the plurality of image sets to display on the display the plurality of modified images included in each of the image sets.