With a bit of luck it's about to change back (on the hour).
It's an ongoing problem whereby briefly Gravatar replaces a user's avatar either with their default avatar (which is the blue and white one you're seeing) or something taken from a random site on the web. It's happened to me and lots of others as well.
AB updates its avatar records on the hour, so cross your fingers!
Same thing happened to me to do. Most disconcerting as it was a risque tableux of women wearing rather less than they should. This was there for a short time then reverted to my usual boring fish. So I too would love to know why.