Honestly, I can totally understand why he made the decision.
First off, personally, I have no desire to see them. I've never been a "Faces of Death" kind of person. Never saw the photos of Sadaam dead. Didn't watch the footage of the people jumping out of the Towers on 9/11. Saw one or two of the Abu Ghraib torture shots, then lost interest. I prefer life.
But also, what's the benefit? Aside from pissing off a few fanatics, what does Obama get out of it?
Who does he need to convince by releasing them? Look at the needless hoops he jumped through to prove his place of birth. Even then, there are still morons who will never believe he was born in Hawaii, even if he had a time machine that could transport people back to his moment of birth. For those people, nothing in the way of evidence could ever be produced, because they want more than anything to believe that Obama was born in Kenya and that the election was rigged. How else to explain the impossibility of a black man becoming president?
These same people will never believe a few grainy photos of Osama resting in perpetual fatility. They were faked, they will say, they're not of Osama. For them, there's simply no way that Obama could have done what Bush failed to do for eight years.
Obama doesn't need to waste his time, and he shouldn't. Particularly since there are bigger security issues to be concerned about. End of story!