<--- IP attorney, but not your attorney
Assuming you live in the U.S. - if the hypothetical movie posters in question are copyrighted (which they probably are) - and you do not own a license to reproduce said posters (which you likely do not) - reproducing them for any use (except fair use, which is a limited exception that probably does not apply in the hypothetical situation) is a violation of federal copyright law. There are stiff (mostly financial) penalities for copyright violations. Many/most people who disregard copyright law do not get caught, but those who do are usually not pleased with the ultimate outcome.
FYI - the bulk of the cost of a framed movie poster is usually the frame, not the poster per se. If you want to steal from someone (and that is what ignoring someone's copyright is), steal from the thieves who charge ridiculous money for framing a picture.