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.