how to add avantar when registre or update your profile

How complicated would be to have an option to add an avatar for user when they fill out the registration form or when updating their profile?
I browsed through different forum threads but I was surprised that I couldn’t find anything related.

When using Quip avatars are displayed by default (you could set it up not to show if you like - which I do at this point)..
So, how users could upload their avatar?


Any help is welcome,
Ivan

I was going to post an example, but don’t think I need to.

http://rtfm.modx.com/display/ADDON/Login.Using+Pre+and+Post+Hooks