Without Banisters makes several good points:
[W]hen images do show torture or execution actually happening, not just victims' bodies afterwards, they encourage us to feel enraged at the people doing it -- but those people are invariably low-level operatives, not policy-makers. And so (as essentially occurred in the case of the Abu Ghraib photographs, for example) those powerful decision-makers who are actually responsible for the system of abuse trot off into the sunset while a handful of soldiers or prison guards get labeled "sadistic" or "bad apples" and get thrown in prison. It's just never going to be photos that implicate the people at the highest levels -- that requires different kinds of sources, much less sensational but nevertheless enormously important. There's a reason tireless French anti-torture campaigner Pierre Vidal-Naquet described the entire anti-torture movement during France's Algerian War as boiling down to "a passionate quest for documents."
This isn't to say images aren't exceedingly valuable. They are. As I've said before, cell phone cameras -- and the existence of the Abu Ghraib photographs in particular -- are one huge reason for the differences between the American conversation about torture for the past several years and the French conversation (or, more often, non-conversation) about torture during the Algerian War. I believe that Obama ought to release the photographs. But ultimately photos can only be worth a thousand words when they're framed by lots and lots and lots of...words.