The image shows a wolf howling at an invisible moon – presumably a reference to the "wolf pack" moniker that the franchise's characters adopt in The Hangover.
The Hangover: Part III: Bradley Cooper, Ed Helms and Justin Bartha will head to Tijuana, Mexico in order to rescue Zach Galifianakis from a mental hospital. The movie is set to hit theaters on May 24th, 2013.
