The luminance of an image is the measurement of the perceived brightness levels. Intuitively, if two images are taken from different cameras with different lighting, some sort of discrepancy may occur in those areas, which were copied and pasted. In particular, analyzing areas in a forged image which are approximately the same distance away from the lens but have different luminance levels. This analysis is heavily dependent on the skill level of the person creating the forgery and the resources available to perform the manipulation. Newer versions of image processing software make it easy for even a novice user to create forgeries based on automated "auto-brightness" adjustments. We succeeded to identify such image forgeries.