This is a very serious question: I've seen lots of threads here about gravatars but I couldn't find and answer to this question: what computer identification/authentication (?) problem, if any, are gravatars supposed to solve?

Neither the Wikipedia entry nor the official website are very useful. The official website mentions a "globally unique" picture. Unique in what sense? As far as I can see it's only the hash that is unique: two persons can have two pictures looking very similar if not identical.

Note that this question is not about which problems do gravatars unarguably cause (like leaking 10% of the stackoverflow.com accounts email addresses like discussed here : "gravatars can leak email adresses" ) but about which authentication (?) problems, if any, are gravatars supposed to solve?

Is the goal just to have a cool/funny/cute icon and save bandwith by having it stored on a remote website or is there more to it, like serving a real authentication purpose which I'd be completely missing?

Note that I've got nothing against them and find them rather cool, but I'm just having a hard time figuring out what their purpose is and if I should care or not about them in the webapps I'm developping.