I want to print some posters but don't know where to look for Images which are not Copyrighted?

I started a new website for selling posters of Movies, Celebrities and Sports. Problem is most of the images that I got from Internet are now claimed by some people that they have copyrights of the images. I am trying to find the right Images but its very difficult for me. I looked in many free stock images website but was unable to get Images which are worth printing.