When a user registers to a Vanilla Forum and doesn't upload a profile picture, a Vanillicon is automatically created. What's a Vanillicon? It's a unique avatar that's created based on the username entered.
Vanillicons have been in use in Vanilla Forums for a long time, in fact, over 300,000 of them have been created so far. Now anyone (or any application) can create a Vanillicon at Vanillicon.com.
Check it out!
Vanillicon is a free service with no limitations. If you would like to use vanillicons in a web application you are building, all you need to do is request the vanillicon directly in your app. To request a Vanillicon like a normal image, provide an md5 hash of the unique ID and specify the image size:
http://vanillicon.com/<md5 hash of email or username>_<image size>.png
Image sizes are 50, 100 or 200.