Agreed.
They seem to me not to be "trophy pictures," as the people in the photos are mugging for the camera in humorous poses rather than trying to look heroic.
Right again.
I would be interested in knowing who instigated these pictures, and for what purpose. This does not negate the obvious criminality of the pictures, but rather seeks to know if there is something going on in addition to what is obvious in the photos.
The most likely explanation is that we have a group of very deranged people who want to show their buddies back home how they treated the "enemy". The picture taking was likely the culmination of a period of increasingly-disturbing actions on the part of these guards.
Another possible (albeit less likely) explanation is that this was part of a concerted effort to break other prisoners quickly. Still wrong, and in some respects worse, as it shows that this was a concerted/condoned effort involving many more people.
What I find totally improbable are some of the claims I've seen trumpeted on this site that leftists have infiltrated the military and undertook these actions simply to harm the current administration.
Now stranger things have happened, and he might simply have gotten a rotten assignment from his company and got out as soon as he could find other work. However, that bit of information did cause me to raise my eyebrows slightly.