How do you tell a print from a poster If the picture is framed and paper covers back.
A poster is also a sort of print. But I assume you mean how you can tell if you have a lithograph or a poster? If this is not your question please ask a follow-up.
When a lithograph is done the paper is runned through a press several times. One time for each color and you will be able to see that the colors are different on the lithograph than on the poster. You need a lup to see this.
Often the posters are also made on cheaper, blank paper but this is not always.
Best Regards, Soren