I think the visal images are used to back up the fact that this is a monumnetal event in world history. It's not commonplace for former national leaders to be executed, and given the war and resulting international chaos, this execution is groundbreaking, and the media will use every means available to ensure that its impact is comensurate with its effect.
I don't think it's designed to prove the execution to sceptics, or to pander to the wishes of those who wanted to see Sadam die - i think it is an historically monumental event, captured for the world to see in our increasingly visual age.