...can't seem to find it under any of the account settings....

 

Here is a how to on it:
https://acurazine.com/forums/3g-tl-photograph-gallery-96/how-post-your-favorite-pics-avatar-556986/

You can use a photo hosting site such as imageshack.us or photobucket.com

Also you may not be able to post an avatar due to your join date, I believe there is a 15 day wait after joining.

 

Ahh....yeah probly the 15 day deal, I don't have any avatar settings showing under my account - thx