This is one of a series of questions submitted by attendees of the Copyright, Common Mistakes and Myths Webinar and answered by Laura N. Gasaway, author of Pocket Copyright Guide for Publishers.
Answer: Well, the copyright status of a meme depends on the source. Assume it is a photo with a caption; was the photograph taken by the person who posted it? If so, that person owns the copyright and can post it with no problems. But if it is simply a caption on a photograph taken by someone else, posting it is copyright infringement.
In other words, the addition of the caption did not transform the photograph into a new work. In December of last year, Facebook announced that it was going to post links to more articles and allow fewer things to be posted that had been published elsewhere. I am not sure how well this has worked out, though.
Pocket Copyright Guide for Publishers by Laura N. Gasaway and edited by Iris Hanney contains information vital to the publishing community.