[@robkk Moderator 11 years, 6 months ago]

for gravatar they would sign up and just add an avatar .

if the email they signed up with on gravatar is the same as their email they used to sign up on your site then their gravatar will show up on your site.

There is also this plugin to allow people to upload avatars to your site.

https://wordpress.org/plugins/basic-user-avatars/