Depending on your interest and what programming languages you know, there are a few options to contribute to Libravatar:
Plugins / Libraries
We want to see the Libravatar community grow and one of the best ways to do this is to expand the range of applications supporting Libravatar out of the box, or with the help of a plugin/extension.
Please consider writing a patch, plugin or extension for your favourite web applications. There might already be a library for the relevant programming language. Otherwise, you could always write one!