I guess you could technicly prevent users from having the avatar (url wise). But thing also is, sometimes you just don't want that.

9/11 was such a moment, where half our community switched to a black avatar that a user of the community put up.

For some things technical solutions are just not the thing. You can't get too technical when it comes to actual content or it will bite you.

[Linked Image from siemons.org]