I think posting memes is perfectly OK, most people add there own captions to images provided on a site to create memes, or even upload their own images to caption and share. I think this is perfectly fair to do, and is a more simple way to reward those who love making/ viewing memes. It's kind of similar to music in that a lot of music contains samples and is intact based upon music rhythms from years ago...is it still original, it's debatable of course.