IIRC, it is opt-in for Google Photos (something like Photos -> Settings -> Group Faces), but that's you the uploader consenting, not the person whose's face it is opting in. The person in the photo need not even have an online presence at all, so there's no way to actually ask them for permission. (In FB's case, they can do it if the other person is a FB user)

What's your definition of biometric data? if I cluster by eye-color, is that biometric data? "Show me everyone with green eyes". Have a run afoul?