If I'm right, I think you have to submit custom avatars to Auran using their helpdesk form. (www.auran.com/helpdesk)
If they deem it appropriate, they will upload it on to their server. after which it becomes selectable in the avatars section.
If, on the other hand, you're after a banner on the bottom of your posts, you have to host it on a web server and reference it in the signature section of your profile
you also either need to have created it yourself or gotten the authors permission for auran to use it.
all the ruls and regulations about submitting your own is in the CoC.
