A CPU 200 analyzes inner region pixels IP and outer region pixels OP independently; compares an inner luminance distribution characteristic i.e. a luminance distribution characteristic regarding the inner region pixels IP with a reference inner luminance distribution characteristic regarding image data of a backlit image that is previously stored in a HDD 202; and thereby calculates an inner similarity Si. Similarity, the CPU 200 compares an outer luminance distribution characteristic i.e. a luminance distribution characteristic regarding the outer region pixels OP with a reference outer luminance distribution characteristic, and thereby calculates an outer similarity So. The CPU 200 then calculates a total similarity St by multiplying the calculated inner similarity Si by the outer similarity So. If the total similarity St is greater than a criterion similarity Stref, the CPU 200 judges the shot image to be a backlit image.