1. An image processing apparatus comprising: a first detector configured to extract a pattern of a color filter array from captured image data for each first unit region, and to detect a first altered region from disturbance of periodicity of the pattern, wherein the first altered region is an image region in which copying has been performed from image data different from the captured image data to the captured image data; a second detector configured to extract a feature amount of the captured image data for each second unit region different in size from the first unit region, and to compare a feature amount for the each second unit region to detect a second altered region, wherein the second altered region is an image region in which copying has been performed from the captured image data to the captured image data; and an output section configured to output information concerning the first altered region and information concerning the second altered region as alteration detection results in the captured image data, wherein the second detector detects the second altered region based on the captured image data from which the first altered region is excluded, and wherein at least one of the first and second detectors is implemented using a processor.