A method for automatically controlling image brightness in an image photographing device by calculating a histogram for an image; obtaining a brightness average for the histogram; determining if a number of pixels of a histogram distribution within a first range and a number of pixels of a histogram distribution within a second range are included within a preset range; and when the number of pixels of the histogram distribution within the first range and the number of pixels of the histogram distribution within the second range are included within the preset range, as a result of a determination, adjusting the brightness average to be a reference brightness.