You can do this with a raspi and a cheap security camera using open source software.
It is effectively already free.
I’m sort of curious why people haven’t already done this, when user fed tracking networks for planes and boats exist. Presumably the much more clear invasion of privacy is a part of it.
It's really only interesting if you have access to camera footage from lots of places, as well as some means to tie faces back to their identities. Every social media company has this already, and probably loads of downstream parties are getting some version of it as well.
