1. A method for automatically controlling image brightness in an image photographing device, the method comprising: 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 is included within a preset first range and a number of pixels of a histogram distribution within a second range is included within a preset second range; and adjusting the brightness average to be a reference brightness when the number of pixels of the histogram distribution within the first range is included within the preset first range and the number of pixels of the histogram distribution within the second range is included within the preset second range.