oomis, you wrote, “I think, though, that when posing in general, if one thinks pleasant thoughts (sorta like Peter Pan), that it will show on his face, and therefore also on the photo, even if he is not smiling.”
I think that is true of some old photos. Lincoln was extensively photographed, and in some of his photos he does seem at least content. But the strain of holding a pose for 15 minutes or more can make a happy person seem less so.