The two guys standing in the front row wearing black are part of a tankcrew. It could be they put their caps on the wrong way because that makes is possible to use the optics in a tank (otherwise the visor would hinder them). That does not explain why the other are having their caps on this way too. They are not wearing a panzer- or Stug-uniform as far as I can see.
Secondly the uniforms are most definatly not being worn conform regulations. The man on the front row, center, should be wearing his EK1 in the center of his breastpocket, not on the flap. The guy on the front row, closest to the camera, seems to be wearing a ordenspange. That shouldn't be located where he's wearing it either and in fact I'm not even sure he should be wearing it on his panzerwrap to begin with.
Thirdly the guy on the front row, closest to the camera, is standing at attention (look at his left hand). The others are not. That seems strange too.
A very interesting picture! Hope someone who is more knowledgable than I am can explain these things.
edit: the guy on the front row, center, wears an almost square badge on his collar. Could that be SS? Would fit with his beltbuckle which looks like the round aluminium version for SS-officers and he's wearing a Schirmmutze for (SS-?)officers too. But his collartab does not look SS to me (considering his rank is should have three or four silver pips in it, which I can't make out on the photo)..