Support for federated avatars using pyLibravatar
Here's a suggestion to extend your Libravatar backend and easily add support for avatars hosted on domains other than libravatar.org.
You can make use of the pyLibravatar module: https://pypi.python.org/pypi/pyLibravatar
All you need to do to generate avatar URLs is this:
avatar_url = libravatar_url(email = 'firstname.lastname@example.org', https = 1)