The Gravatar URL uses an md5 hash of the lower-case email address.
So I'd expect my Gravatar to use MD5("")="d41d8cd98f00b204e9800998ecf8427e"
However, my Gravatar actually uses "dfc87203d5c57e2ad21acc178eead605". Where does this value come from?
Since February 2011, Stack Exchange uses a salted hash of your IP address as a fallback to generate your gravatar if no email has been specified.
It used to be an MD5 hash of your IP address. For example, if your IP was
These unsalted hashes are still available in older database dumps.