Brain...hurts...gonna see if I can get this organized... You're doing great!
Okay, so a person who is in very good shape makes him or herself look in poorer shape? they take a picture of themselves in such simulated shape with an newspaper having a specific date? and they label it a "before" picture? Yes, all of this is correct
They then undo what they did to look in poorer shape? Yes
take a new picture of themselves in this shape holding a newspaper that is dated before? after? It's dated after the one in the "before" pic
the "before' picture and they call this the "after" picture and claim it shows the before and after pictures in the real ads can be faked? The pics aren't fake, but it's very easy to do something in both pics to overstate or falsify the effects of certain diets and exercise programs
Is that basically right or is it a mess? You are mostly right with all of this!
And you want us to find out what this other thing the people do to closely duplicate the real photos is? if so, does it involve tape? bodily functions? manipulation of the body? camera placement? "Manipulation" is the closest. Just think about tips people give for making fat people look muscular and/or in better shape...
Do the people doing the simulation of the real ads actually lose any real significant amount of weight or gain muscle mass? NO! In order to expose the flaw, a person needs to be in fairly good if not great physical shape all along. They do something to alter their body in the "before" pic, then usually do two things to alter it in the "after" pic. Pushing their gut out is part of it, and a physically fit person wouldn't need to suck in their gut because it looks like they want it to.