Log avatar changes

Hi all. Is it possible to log when users change their avatar ?

There is no such feature at the moment, we could probably add a text log to say it happened, but keeping the old image is very risky.

I could see this being useful for a website that keeps a local copy of user avatars to display forum contributions on the homepage or what have you. So you know when you need to update that file.

Text log would be enough for my purpose.