That’s why I have lots of angles and objects.I'm not going to get into the argument, but the easiest way to verify size is too show pictures of the measurements or put a common object in the picture as a size reference. If this guy is 6'4' and 300lb, that probably is an 8". If he is 5'8" and 180lb, probably not.
I will say that penises do not always cooperate while measuring and taking pictures. When your thinking about holding a ruler and snapping a picture. You are not thinking about what got you hard.