I think voyeurism should be split into "strong" and "weak" varieties. Weak voyeurism is when the person(s) being watched is already being knowingly watched by other people, and strong voyeurism is when the person(s) believes they're alone. By way of example, if you watch someone in a communal shower (through a peep hole), that's weak voyeurism, whereas if you watch someone who's showering alone, that's strong voyeurism.
Good idea?