If I point a camera into my neighbor's yard and run it 24/7 for 3 months, I'm probably in deep doo-doo even if he has no fence at all. With a fence, I'd refer to Kyllo v. US, though that disturbingly was a 5-4 decision rather than 9-0 :(.
https://en.wikipedia.org/wiki/Kyllo_v._United_States