Any single photo doesn't say anything. Suppose that the photographer was just setting up and snapping off some shots as a test, and Obama was waving to somebody. Then the official photo was taken without Obama waving.

This is how people with an agenda use propaganda.

If this type of thing interests you, you should check out: http://www.badastronomy.com/

Among lots of other amusing stuff, it has great reviews of gaps in reality in many popular movies.

Enjoy!