Probably cause you don't see any Obama photos with him doing that gesture.. eyes, forehead and ears is totally Obama, not to mention that's his logo too.
I'm not really sure I can see Obama in this piece. I don't think he looks like it, even though it's a caricature.
It's good, but you might wanna fix that hand, though. It's wierd in terms of how you have it drawn and colored in.
I have to agree with Fenne; it looks nothing like Obama.