Avatars: mouse-over popup display

[Noosphere]

I'd like to set up my avatars so when users mouse over them the pop-up display---which currently reads "[username's] avatar"---shows the given name of the avatar instead. For example, I have avatars of famous landmarks, and would like "Mt. Rushmore" to pop up rather than "Fred's avatar."

I have over 500 custom avatars done to date, so obviously a global approach would be preferable to having to edit each one separately.

A nudge in the right direction would be much appreciated.