First clue is the side of the cover art. Obvious mirror of the front. There is no reason why the official artwork would do this because the official artwork extends much farther than where the artwork on that cover ends.
Second clue is the blacked out bottom on the DVD cover. They are obviously covering up the credit text found on the poster art.
I would also imagine that they would relocted "The Dark Knight" logo and text (along with the actor names) to the top instead of having it along the bottom.
Do I need to go on?...