Well... noir is a movie genre. Mostly movie's setting is 30's-40's and story is about framed detective. Usually he is one of few good cops and tries to solve a crime while running away from corrupted police. Sometimes it is about cop who has to break law in order to catch real murder. The most famous example would be Max Payne.

Now this exact picture was drawn under impression of Sin City by Frank Miller and Sin City The Movie by Robert Rodriguez.