From my experience, professional photographers, photo lab technicians, and their ilk, who spend lots of time looking photos and their technical aspects (sharpness, lighting, colour, pixelation, etc, etc, etc), would easily spot the, to me, obviously edited photos. Case in point: the top photo in the The Stack article - clinton-fake-photo-832x333.jpg - is so obviously faked that I'm surprised that anyone would be fooled by it.
First dead giveaway: Clinton's head is illuminated from the right-read as is Mandela's(?) head. De Angelis's head? From the top-front. (I can't believe that De Angelis's victims didn't spot that fakery.)
Second less-dead giveaway: the pixelation isn't quite the same. The imposter's pixels are larger, not by much, than Clinton's - at least in the sample from the article.