I love Gravatar, the service that lets me associate my email address with a portrait or avatar that services across the web can then use to represent me when I sign on to their site. The trouble is, not enough other sites use it, so I have to keep uploading an image to every service I use, and not enough of my friends are on it, so I can't easily pull images for them. This all makes it really hard to create visualizations of my social network based on email, since I can't get pictures for most of the addresses.
To solve this, I took Shannon Whitley's awesome SPIURL project that provides permanent and easy URLs for Twitter handles, and created a new service that gives you a simple way to pull avatars images from Twitter, Facebook, Digg and Gravatar, and associate them with an email address.
You can try it for yourself at http://overtar.appspot.com, which has the full documentation. Its goal is to try really hard to find an avatar for a user by looking on multiple services, allow you to specify a custom image if none is found, and then cache the result. It uses Gravatar images if they're available, but if they're not it doesn't authenticate that the person setting an image owns the email address, so it's not a replacement, more a light-weight complement. I have the option to filter out unverified images, but my goal was to make it easy for my application to associate an image with an address.
Here's some examples of it in action:
Searches Twitter, Digg and Facebook for a public picture
The Facebook public profile picture for the user 'petewarden'
A lot of people use the same username across multiple services. Instead of offering your user a blank avatar when they sign up, why not take a guess and pull the portrait for the same username on other services as a default? That's what Overtar is here to help with.