1. An image processing method performed by a processor, the method comprising the steps of: generating chrominance image information based upon input image information; setting a determination target area to undergo determination of a target object within a determination target image constituted with the chrominance image information; calculating an average chrominance value for each of the determination target area and a plurality of peripheral areas set around the determination target area, based upon the chrominance image information corresponding to each area; evaluating color information expressed by the average chrominance value calculated for the determination target area to determine whether or not the color information matches a characteristic color defined in advance in correspondence to the target object; evaluating a difference between the average chrominance value in the determination target area and the average chrominance values in the peripheral areas to determine whether or not the determination target area is an image area separate from the peripheral areas; and making a decision as to whether or not the determination target area contains the target object based upon results of an evaluation indicating whether or not the average chrominance value in the determination target area matches the characteristic color and the result of an evaluation indicating whether or not the determination target area is an image area separate from the peripheral areas, wherein at least one of the steps is performed by the processor.