In the Edit Profile section on the Configure Site > Social Networking page, you can choose whether to use Profile Pictures/Avatars, customize the sizing, and language used.

If you create Avatar Categories and upload Avatars to your website, members wil also be given the choice to choose a pre-loaded avatar on their Edit Profile page, besides the option of uploading their own avatar or profile picture.  Go to the Members tab on the Admin Panel, and you can find the Add Avatar link under the List Avatars page, and the Add Avatar Category link under the List Avatar Categories page.