1. An image processing method, comprising: an input step inputting a processing target image obtained by a shooting optical system; an estimating step estimating an ideal bright point image component included in an occurrence area of a flare in the processing target image; an extracting step extracting a real bright point image component including a flare component from the occurrence area; and a calculating step calculating a difference between the ideal bright point image component and the real bright point image component as an index of the flare component included in the occurrence area.