Like the avatars over at Neopets, avatars are hidden pictures that you can gain around the site there are also default avatars of all pets [as seen in the pictures]. You can view all the hidden avatars you have unlocked at Ziranek or at your profile. Ian is always releasing new ones. You also have your own profile avatar which shows up when people are friends with you. You can change your profile avatar at the Ziranek avatars page. The Digital Fairy rewards you for the number of hidden avatars you have found.
The most up-to-date Avatar site at the moment is Here