The problem is not about the images, but, as Rob pointed out, about the act of spying.
We may suppose of taking a picture of the entire front of a building with a super-duper ultra high resolution camera and there would be nothing objectionable in this, even if, thanks to the high resolution, we could enlarge the details and recognize the figures through the windows. It 's a completely different thing from pointing a telephoto lens on someone's window in order to spy on his private life.
I don't know U.S. laws, but in Italy, the act of pointing a binoculars or a telephoto lens to spy on the private lives through the window is an illegal act (technically "illegal interference in private life"), regardless of whether you do or not photographs.