Actually it's called a Fiducial... When Photo Mosaicing multiple images these fiducial's help align the photo using geo coordinates... Film cameras normally have 8 fiducial's that are used along with control points to place each pixel in it's geo referenced space... In other words the photo is ripped apart and put back together piece by piece by a computer program, Sometimes if you don't have good stereo photo's (Valley and Gaps appear) IE you run out of image and you see the tags of the image... It happens with big Mosaics sometimes.
Each Camera also prints it's id so you can tell what camera took this photo...
Each Camera also prints it's id so you can tell what camera took this photo...