Comment Public Key Encryption (Score 1) 170
What if Gravatar published a public key, and sites displaying Gravatars pointed their image links to encrypt(gravatar_id + random_salt)? It seems like this would solve the problem, since people viewing the page can't get access to the users' real Gravatar IDs. Sure, the forum sites would still see your Gravatar ID, but they already have your email address in the first place.