Google refused my app because app unauthorized use of copyrighted content. How is it possible that Rottentomatoes uses posters in their site and app? Do they pay for each poster? At which organization do I have to pay for posters?
I read a comment here, at some case someone are able to use covers/posters/screencaps under fair use. There are guidelines for fair use, namely the four factors judges are expected to consider in determining whether a use is fair use or not.
App using the material for criticism; not profiting yourself from your post, your use is unlikely to harm sales of the work; and for the screencaps at least, app reproducing only a very small portion of the movie.