The Painting of the Clown in Commissioner Loeb's Office, foreshadows' the appearance of the classic Clown psychopath, the Joker, in a sequel or just in the general mythology that the comic books have set up.
In addition to voicing Barbara Gordon (James Gordon's wife), Grey DeLisle voiced (uncredited) the role of Vicki Vale, who was not in the original graphic novel, although she is mentioned in one of the newspaper articles in the book's first pages as being a "cutie clepto". Vicki replaced several television news reporters used in the original story.
The trivia item below may give away important plot points.
Quite a few scenes and shots from the movie, that were in the original graphic Novel, made it into Christopher Nolan's "Batman Begins" (2005). One notable example include the appearance of the army of Bats at the location where the police have trapped Batman.