It might be hard for you to believe a picture this awesome actually exists, but I really think it’s legit. Why? Here’s the evidence:
A) It’s one thing to match the Joker’s costume pitch perfectly, it’s another to have a full-replica batsuit from the movie.
B) How else do you get an empty main road in downtown Chicago to shoot a funny skateboarding shot?
C) Ledger is (was) a known skateboarder, and there’s a video of him actually skateboarding on set while wearing full Joker make-up (at 23 seconds).
So either this is the world’s greatest Photoshop, it’s the work of some hardcore skateboarding replica costume enthusiasts, or it’s for real. I choose to believe it really is that awesome.