This photo is a GREAT example of how little things can trick viewers.
First of all I have seen the scene with Shane and Jack Napier. I must say I was very surprised at the fact that Shane absolutely DWARFED Jack. I really didn't expect that because I estimated Jack to be close to 10" while Shane I estimated at between 9-9.5" But in the scene it was clear that the two mens' lengths were closer than I thought but shane had an enormous girth advantage over Jack.
So what's up with this photo? Well first off Shane is clearly no where near all the way erect, while this appears to be a full sized Jack. Secondly, it may be difficult to spot to the untrained eye, but the cameraman is NOT in fact "side-by-side" with Shane and Jack. In fact it looks like he is positioned directly to the side of Jack (closer) with Shane off a little further away from the lens to the left. There is tons of evidence in this photo to support this assertion. But in the end just watch the original VIDEO and you'll see what I mean. Shane is significantly bigger.