1. An image processing device comprising: circuitry configured to: perform extraction of a subject image representing a subject from each frame of an input image; detect a size of the subject image; determine whether the size of the subject image meets a predetermined condition; and perform a synthesis process to synthesize the subject image of a current frame of the input image with a previously synthesized image in a case the size does not meet the predetermined condition and terminate the synthesis process in a case the size meets the predetermined condition.