To answer the original question; it all depends on the situation.
How could you possibly conceive guidelines for that kind of situation?
Does any particular member ‘owe’ the community picture proof after X time on the board, n gains, or y size? We could write a formula I guess, but what’s the point?
What somebody thinks is unbelievable or impossible might well be true or real. Or, it might not be so special for other people. It’s a matter of perspective.
The legitimacy of PE will never go down - there is already enough evidence don’t you think, that it does work? The accumulation of stories, member pics, size’s database, personal experience, and many other sources should be enough to convince even a harsh skeptic that it does work - to at least some extent.
Imagine the scale of conspiracy if literally tens of thousands of guys over multiple websites and forums were all tied to some elaborate scheme? It would cost more money to impliment that you would make from it!
Back to the first issue - do you really think that even the clearest photo proves anything, for the reiteration of the points listed by others? It is just a nice little reassuring piece of data that some doubters can look at and feel less lied to (or completely lied to, depending on the quality/obvious falsity of the image) A small piece of a puzzle that you put together in your own head on each and every member, composed of their stats, story, gains, pics, and even general manner etc. They all contribute.
It’s not unusual that someone will fake for whatever reasons - there are thousands upon thousands of examples online everywhere you look. We will never stop this, even if pics become mandatory for your avatar ;)
Misrepresentation - who gives a flying fuck? If there is some guy who is bothering you because he claims rediculous size or gains, ignore them - they will dig their own grave if they are liars. The truth is that each little inconsistency will accumulate on the pile, and eventually somebody will call them out and they will be disgraced from the entire community.
It has happened before and it will happen again. Nobody (except twat) is a good enough liar to keep their story believably consistent for years on end. I could give an example but it would probably be recieved badly :D
Like mem said, keep to yourself and just thank your lucky stars you are not a poor newbie, who doesn’t know the full story and is suckered in by a bullshit guru.
I despise liars, but it is all too common a thing. Do as I do and just set their dickhead attribute bit to 1 so that you enable a bullshit filter on every input you recieve from them, and go on with your own life.