As per the original Tolkien, the story of The Hobbit is the story of Bilbo Baggins' transformation from a placid homebody to a bold and cunning hero. One of the key turning points is captured in the latest still from the movie adaptation.
So, you might consider the following image a spoiler. I don't think it is, but you probably shouldn't read my subsequent comments if you're looking to stay fully fresh.
That, I believe, is Bilbo drawing his sword out of the carcass of a spider in Mirkwood. This is the sequence in which Bilbo uses the ring to outwit the spiders of the forest, slays them and rescues the dwarves. This is when he first stands up for himself, physically, without the support of his cohort.
He calls the sword Sting, naming it at the end of his battle with the spiders. We could well be looking at that exact moment.
The pacifist in me feels a little odd about this step in the "hero's journey", but in The Hobbit, at least, there's also another storyline being traced, that of Bilbo's relationship with the ring, the seduction of its power, and his slow decline. You can read his use of the ring here in Mirkwood, and its association with the killing of the spiders, with Bilbo's eventual near-ruin.
The picture was published by The LA Times. They also provide some interesting quotes from screenwriter Philippa Boyens. Here's a juicy bit on the tone and target audience:
The story is very much a children's story so deciding how to tell this was one of the first things we had to do. Who is the audience? It is very distinctly different, tonally, to Lord of the Rings until the very end and then you begin to see the world of Middle-earth opening up… but, having said that, we felt that it is the same audience [who will come to see the films] and then you start to worry because it is easy to repeat yourself. It is quite a similar journey, you're going from the Shire to a large, dangerous mountain.
You can expect to see Bilbo vs. the spiders in An Unexpected Journey, the first Hobbit film due in December.