That's such a magnificent question. I so often focus on federal cases in my legal research that I forget that mostly federal cases are about people vs government and not as often (though they exist) people vs people.

The main thing that I was basing my background here on was the fourth amendment, which is pretty strictly people vs government.

I've been doing some searching on this issue, it seems that this particular type of law is mostly done at the state level, for instance in California:

California Penal Code 647

(i) Who, while loitering, prowling, or wandering upon the private property of another, at any time, peeks in the door or window of any inhabited building or structure, without visible or lawful business with the owner or occupant.

(j) (1) Any person who looks through a hole or opening, into, or otherwise views, by means of any instrumentality, including, but not limited to, a periscope, telescope, binoculars, camera, motion picture camera, camcorder, or mobile phone, the interior of a bedroom, bathroom, changing room, fitting room, dressing room, or tanning booth, or the interior of any other area in which the occupant has a reasonable expectation of privacy, with the intent to invade the privacy of a person or persons inside. This subdivision shall not apply to those areas of a private business used to count currency or other negotiable instruments.

(B) Neither of the following is a defense to the crime specified in this paragraph:

(i) The defendant was a cohabitant, landlord, tenant, cotenant, employer, employee, or business partner or associate of the victim, or an agent of any of these.

(ii) The victim was not in a state of full or partial undress.

So these are specific to people, and these laws are called "peeping tom laws" (for obvious reasons). I'm curious how law gets applied to objects that you own that can tell you about a person that invade your privacy (dildos, for instance), but I can't really find much (then again, I am not a lawyer).

If they're outside your property, you can't stop them taking a photo of things visible on your property.