You can load an image as your "avatar" (or use one of the 'stock' images that are available) by going to My Home and editing your personal information. You'll find the avatar information near the bottom of the profile options. If you upload your own picture, it needs to be no more than 80x80 pixels and in .gif, .jpg, or .png format.

The picture you see as my avatar is my dog, Mysti, in 80x80 pixels!