1. An image processing apparatus comprising: skin-tone image area detecting means for detecting a skin-tone image area, which is contained in an image represented by applied image data, based upon image shape or image structure; gray pixel detecting means for detecting gray pixels contained in the image represented by the image data based upon color information obtained from pixels that constitute the skin-tone image area that has been detected by said skin-tone image area detecting means; and color temperature estimating means for estimating color temperature of a photographic light source based upon gray pixels that have been detected by said gray pixel detecting means.