[UPDATE: Oops, sorry folks, it's been pointed out to me that this pic is NOT new. My apologies... I try to stay on top of these things but I hadn't seen this image before and assumed it was new. Do read the rest of the story, though!]
There's a rumor (this hasn't been confirmed by Warner Bros.) that there will be a seven minute preview of The Dark Knight playing in front of Will Smith's upcoming sci-fi film I Am Legend, but only in IMAX theaters. No doubt they're doing this because parts of The Dark Knight are being shot in the super-hi-res format.
For certain movies I always try to catch the IMAX version if it's available. I think that IMAX to regular movie theaters is like regular movie theaters to big screen TVs. :-)
The preview is supposed to revolve around The Joker. As BOF pointed out, since I Am Legend opens in December it would make sense that it will be Joker-centric due to the hidden message in one of the viral websites that came out this summer to promote The Dark Knight. If you recall it said "See you in December!".
Finally, I haven't seen that particular image posted anywhere yet so I thought I would toss it up for you guys.