I can understand staged pics for propaganda purposes, but why did nazi authorities allow the pictures taken of human mass graves, people hung, shot etc when it was these same pictures that would later be used as evidence to convict them at trial?
Apologizes, i am on mobile, ill fix editing when i get to a PC.
Depending on the time of the war and the camp, they did and didn't, at the beginning of the war, when it looked like they would win, some pictures were taken to prove what happened and also sadly for personal mementos. As well as this, some prisoners were able to smuggle cameras into ghettos and took pictures, hence why we have some images of ghettos.
From my knowledge, the overwhelming majority of images came from either British, American or Soviet photographers. While Soviet photographers took mostly propaganda "scenes" brits and US photographers took pictures simply of what they found.