This is just the trouble,I've yet to hear of an expert who is 100% right in their field. It takes years of the practical side of work as well as attending college/uni and studying books. Passing a few exams doesn't equate to being a fully-fledged anything,it's experience that counts,and someone in their late 20's or even 30's can't possibly be experts when it comes to diagnosing mental illnesses just by either looking at them or reading about certain traits in that person. MANY people " look " like psychopaths,also MANY people have the same idiosyncracies as Jeremy,but I certainly wouldn't like to bluntly say,without having met that person or had a face to face conversation, that anyone was a psychopath.
As for photographs,I'd say that the " sitters " are far more relaxed and comfortable than of years gone by when I think they were possibly told not to smile back then,this is why I find the one where Jeremy is smiling,is of a self-confidant young man who thought he could get one over on everyone. Sadly,it went all wrong,for I feel sure that he,himself,because he'd told the truth,thought that things would be alright.
Then again,if he'd appeared solemn,it would have spelled admission too,as anyone who is,and happens to hang their head,or hide from the crowd,usually are guilty as that's how they display their shame.
I have yet to meet anyone who is believed to be 100% right in their field of expertise, especially when they views don't correspond with those who disagree with them. I concur entirely that a degree -on its' own- won't equip but MOST are required, as part of their course work, to spend time working with skilled professionals to gain practical experience.
I have had past experience of a psychopath of the non murdering type and with hindsight it's easy enough to see. In the video the smile Jeremy gave from inside the car chilled me to the bone. The last time I'd seen that shot was when it happened -and I had no experience- and I thought he was smiling at someone he knew. Seeing it now I can see that he wasn't. The smile was put on like a mask. Too big to be real, it didn't reach his eyes and was cold as ice. Like you, I don't think it any more possible to tell a psychopath from a picture that it is to tell a criminal from bumps on their skulls but I DO believe it's possible to make an educated guess when you know someone's MO.