I'm no expert on posters but I think they can be a little tricky to authenticate. American Pickers (an antiques show) said that genuine old posters were made of very thin paper. They were meant to be used and discarded and not displayed and collected over long periods of time. They were not meant to last forever. So, reproductions are usually made of thick, poster-like material. Are you able to post pictures? Are you able to take them out of the frame? If they are brittle and thin, don't bother trying to take them out, don't want to damage them. You may even be able to use a magnifying glass to see if it was printed with millions of tiny dots (like a printer). Hopefully we can find some good sites for you, I hope they are really old!
