That's the point: filming should be opt-in.

What does that even mean? You have to opt in to film?

If you meant to say "to being filmed", how do you implement that? People have been filming crowds since the 1950s; "Candid Camera" famously made covert filming mainstream.

"Should be" is a dream of the Good Ship Lollipop. Here IRL, laws and regulations are the only thing that will discourage it.

You can't do it with technology alone (or really at all). It has to be the law that does this.

Yes, laws and regulations are how you would make something opt-in. I don't see the problem, but thanks for the downvote I guess?

This opens a huge can of worms.

Dash cams would effectively become illegal.

Someone just wanting to record themselves and some friends doing something would need to ask explicit permission from everyone in the background.

It's just not a tenable option.

Perhaps one should look at the laws in place in the regions of the world where this is already true to see examples of how these worms can be handled.