There's nothing in the rules prohibiting furry.
Regarding attachments, the site rules say this:
"No copyrighted/pirated content is to be hosted on our system.
We'd also appreciate you not hosting random images you can easily find on Google images or whatever other image collection site on our system. Mass storage is cheap when you buy it for your personal machine, but it's not when you're leasing high-availability hardware. Lots of sites will host your shit for free and hold on to it for damn near forever. When posting, there's an option to remote upload images. This will post your image to a random private IMGUR account. Use this for posting random screenshots and the like."