The case I cited specifically talked about government doing it.

For facial recognition or just plain photography? Obviously Katz predates the former.

Katz jut said "what a person knowingly exposes to the public" IIRC. We'd need a new SCOTUS case to clarify whether data derived from physical features that can be used to identify you still counts as such

Agreed.

> what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.

Identity might be, might not be.