Gravatar is an attempt to allow users to have one globally recognized avatar. The service, around for several years, allows a user can set an image as an avatar and have it recognized on a variety of sites. Later, users can change an avatar once and have it change on every Gravatar-enabled site that they use. Though the service is somewhat well known, what is not is its robust API for developers to integrate the Gravatar service into their own sites.
Using the API is pretty simple, as it requires no API key or authentication. It sends a surprising amount of response types, including JSON, simple XML, PHP, VCF/vCard, and QR Codes. It is a RESTful service, like many good APIs. To make things even easier, they have code samples for a lot of common CMSes and languages, such as Ruby, Ruby on Rails, Python, Django, and Java.
The video embedded below shows how Gravatar explains its service:
A large number of sites have already integrated Gravatar, including WordPress.com, IntenseDebate, VideoPress, and Polldaddy. If this gets sufficient support, it could make it so the first step when registering at a site is no longer uploading a new avatar every time. Saving time in such a simple way is always a good thing, in my eyes.
A similar service, built off of Facebook and Twitter APIs, was hacked together at The Next Web Hackathon.