Why did the CIA take photos of “detainees” before sending them off to be tortured?

To humiliate them and help induce the desired state of “learned helplessness” before interrogation was probably one objective. It likely was also a CIA CYA operation – enabling CIA operatives to document that – however broken the detainees eventually became – “the prisoners were healthy as a horse when we sent them off.”  This constitutes additional evidence that the basic reason prisoners were “rendered” elsewhere was … you got it! – for torture; and that those insisting on the “BEFORE”-photos were fully aware of that.