Enable User Avatars/Picture Support

First off, you should really search through drupal.org because this has been asked (and answered) a million times. While Drupal Documentation is present on drupal.org, it is hard to find what your looking for sometimes. I find that google works better than drupal.org search most of the time.

Anyways,

Go to Administer > User > Settings and enable "picture support"

Hope that helps!