In last week's episode, "The Man Behind the Curtain", Ben appears to be speaking to an empty chair, where Jacob should have been sitting. Locke is skeptical about the situation and has started to think Ben is crazy. You heard the "Help me" line and Jacob's wrath throughout his little hut, but perhaps you missed the screen flashing for a short second with the above image, which is likely of Jacob himself.

Why does Jacob only appear for a second? Why does he say "help me"?

The image we have of him leaves many possibilities. It's hard to tell whether he most closely resembles Alvar Hanso, Locke, or any other character one could make an argument for.