The photo, depicting a tender moment between Betty and Hulk among a throng of spectators, is obviously post battle, and clearly shows an open wound bleeding gamma green blood.
In the comic books, the Hulk only bled on rare occasions, usually when fighting a superior foe. In fact, it is believed that he has a gamma-powered healing factor similar to Wolverine, yet so hyper-fast that it seems as though his skin can't be punctured by normal means (blades, bullets, shells, missles, etc.), but in actuality it's just healing faster than the naked eye can see.
So, why is the Hulk bleeding in this photo? It's probably due to a combination of battling the Abomination, and bodily exhaustion to the point where his healing factor is compromised and not working at maximum efficiency. After all, the Abomination is as strong or stronger than he is.
(GEEK SIDENOTE: Technically, the Abomination is stronger than the Hulk only when the Hulk is at rest, or "not angry." The Hulk's strength grows when angry or under extreme stress, and is considered limitless. Logically, it follows that as long as the Hulk can keep getting madder and/or stay angry for a long period of time, his maximum strength is incalculable. That ability is unique in the Marvel Universe. So, as the Hulk himself announces from time to time, "Hulk IS the strongest one there is.")
The current
Marvel Universe character database, while condensed from earlier versions, describes Hulk's damage resistance in this way: "The Hulk has shown a high resistance to physical damage nearly regardless of the cause, and has also shown resistance to extreme temperatures, poisons, and diseases in addition to regeneration of damaged or destroyed areas of tissue at an amazing rate."
Another theory (and the most likely one), is that the movie makers simply wanted to convey that the Hulk has undergone some major trauma without having to explain to the non-geek audience the whole healing factor thing. Lets face it, Hollywood always chooses the "more believable" scenario in comic book movies, and admittedly, it would slow the movie down to have to kowtow to the geeks like me who obsess over every little deviation from the comics.