Does iOS have switch to disable saving location inside photos?
I'm not sure. I don't actually have any iOS devices.
Looks like it is possible https://www.igeeksblog.com/disable-geotagging-for-photos-on-iphone-ipad/ but nobody does it.
Is it possible to watch "Take Photo" event from application? It would be nice hidden service to watch user :)
I don't think it's possible to watch it in the background.
Interesting idea of retrieving user location history without explicit location permissions:
https://github.com/KrauseFx/detect.location
What's even more interesting is that you can potentially retrieve user location for a period even before the app was installed.