Thanks for the responses, folks. It sounds to me like the guard in Chiller's case was full of it. A private security officer (at least in the US) cannot legally fine you, detain you, or do anything other than ask you to leave or call the police. If the guard was a real law enforcement officer, he could arrest you or cite you, but not fine you directly. As for my own situation, I think I'm going to keep doing what I've been doing. I've got better things to do than seek out the owner of every building I want to photograph. I haven't yet actually been asked to leave, although one guy was really suspicious of why I was taking pictures of some coils of wire he had stacked up next to his factory. He thought I was working for his competitors or something.