This function does not work correctly for me. The generated Gravatars do not match the ones actually produced by using the corresponding address.
The problem was traced to differing output from the
From version 7 I get:
IntegerString[Hash["firstname.lastname@example.org", "MD5"], 16, 32]
Version 8 users apparently get:
Why do I get a different result and how do I get the right one?