How can you tell the difference between officially licensed movie posters and fake ones?

I'm trying to find official UK-style (61cm x 91.5cm) posters for some Nolan films: Batman Begins, The Dark Knight, Inception, The Dark Knight Rises, Interstellar and (when it is released) Dunkirk. I'm just worried I'll get a fake poster instead of a legitimate one. If all else fails, then I might have to find the digital versions of the official posters and pay to get them printed. via /r/movies http://ift.tt/2uOzWwV