This question already has an answer here:
As for me - Gravatar does not work at all. I can't change my last gravatar to a new one, I always get 'Whoops! Something went wrong!'. I even can't file a bug, I can either read FAQ or 'ask community for help'. It seems that Gravatar developers are very reluctant to do any technical support.
Therefore, I think Gravatar doesn't deserve to be the only viable alternative in SO Careers as it is now.