It looks like it pulls data from the "backdrops" section on TMDb. See the movies.io page[0] for a movie and its corresponding[1] TMDB page. There's also a TMDb API method to get a list of all the relevant images in XML[2].

[0]: http://movies.io/m/jf [1]: http://www.themoviedb.org/movie/61791 [2]: http://api.themoviedb.org/2.1/methods/Movie.getImages