also, considering the comic is titled "Batman: The Dark Knight FALLS" and not "...Returns" this is obviously fake.
Not that I think this is either real OR a good idea, technically, "The Dark Knight Falls" is the correct title. When the series was originally released in comic book form, the series was simply called "Batman: The Dark Knight." Issue one was "The Dark Knight Returns," issue 2 "The Dark Knight Triumphant," issue 3 "Hunt the Dark Knight," and issue 4 "The Dark Knight Falls." It was only when the series was collected into Trade Paperback form was the title of the series was from then on called "The Dark Knight Returns." Being that issue 4 is the one which featured the Superman/Batman fight, whoever photoshopped this up is pretty clever, as it makes it seem somewhat authentic.
The fakeness comes from 1) the Robin from DKR was the female Robin Carrie Kelley, and 2) there is no way ANYONE in this production would cast Bieber for even a cameo role as "random dude getting killed." Unlike a musician who has shown acting chops like Justin Timberlake-who said he wants to be the Riddler, but being that this is a Superman movie featuring Batman, plus more than likely Justice League films before any new solo Batman films, unlikely anytime soon-The Beebs has shown no acting talent aside from acting like a royal douche. So, no cause for concern here!