How do the SE sites know when I changed my Gravatar?
The SE sites directly link to these Gravatar images from gravatar.com, so that when it is updated on Gravatar, it will be updated immediately on the SE sites as well. You may need to clear your cache to see the changes, though. According to Gravatar, your email address is hashed and used in your avatar’s URL. For example, in the URL http://www.gravatar.com/avatar/6b40908a8b13c9c7eecfcb95960cc0f6?s=128&d=identicon&r=PG, the portion 6b40908a8b13c9c7eecfcb95960cc0f6 is your email’s md5 hash, provided you have an email address associated with your account.
