Thankfully, as far as I know, nobody has ever entered that many pictures of their chicken, and I'm sure their chickens has thanked them.
On the limit itself, there is an unsaid limit of 50 images per a post in a thread and in an article page (and most likely in a PM post, but I haven't tested that out yet). On an article, there is a secret trick around that limit so you could post more than 50 pictures on a page, but I don't know if it works for thread posts yet because I haven't tested that either. Either way, we do need to set a limit for this contest because we do permit multiple pictures to show how bad the chicken is molting, but don't want so many that even the website can't handle it.