Lastly, I think he might appear to be smaller in that pic because his balls are pretty retracted. Usually when that happens you lose about half an inch of "optical" length. To see this, compare the difference between where the topside of the penis ends and where the bottomside of the penis ends (it's where it hits his contracted balls).
If you were to crop and look just at the topside of the pic, you coudl easily guess "5 1/2"
If you factor in the bottom though, it really is like 4 1/2" between his balls and shaft.