I do not believe that it would be possible to prevent this sort of behavior by force. Any script kiddie could pull this off, and there are more born every day. Some of them barely even understand Western values, let alone have an incentive to value them.

Rather than (edit: in addition to) relying on protection, we should rely on personal safety practices. Using our own portraits as avatars may have been a mistake, in hindsight. I will recommend to my friends, that they teach their children to use a photo of their favorite toy or something, instead of their own face.