That's uh, kind of how you greet people in Japan. I did it too when I had to, its considered rude if you don't. But the way he's bowing is way too low, its more of a low head nod than a full bow nowadays, especially if you're shaking hands. They've kind of "Americanized" it, as my college roommate said. It's really a sign of respect rather than a sign of submission.
Having said that all that, that picture is offensive, if intentional. Why? Look at the length at which they bowed their heads the emperor's and the President's, Obama's is much lower and that is a sign of submission whether he knows it or not. The President and the emperor being of the same "rank" in terms of world leaders they would have bowed the same length, which would have been proper. I mostly attribute that to a lack of knowledge on behalf of the President. Big surprise huh?
Shyukan no jugyou wa owarimashita. Mata ne.
(Culture class is over. See you later.)