1. A non-transitory computer-readable recording medium having stored therein an evaluation program, the evaluation program causing a computer to execute a process comprising: calculating a background difference amount of each of a plurality of frames obtained by sequential image capturing as a number of pixels that are included in a frame and a difference between brightness of which and background data calculated from frames that are obtained before the frame is larger than a threshold; detecting, from among the plurality of frames, beat frames, wherein the background difference amount of a beat frame is smaller than background difference amounts of frames sequentially obtained just before the beat frame that continually decrease, and the background difference amount of the beat frame is also smaller than background difference amounts of frames sequentially obtained just after the beat frame that continually increase, the beat frame indicating a timing at which a person displayed in the plurality of frames takes a beat; and outputting an evaluation on a rhythm of a motion of the person based on a rhythm indicated by the beat frames.