If they were doing a bunch of murders secretly it’d make zero sense to be taking pictures of everyone

It makes sense from a bureaucratic perspective. Industrialized genocide isn't a one-man job. You've got supervisors on top of supervisors, all looking over each other's shoulder to make sure their department goals are being met. Photos of individuals being massacred makes sense for a whole host of oversight reasons.

But its a huge leap from mug shots to genocide. It just doesn't matter to people who can sell "Ghost of Chicken Kiev" to a credulous public.