Or what about: the photographer tries to hide so that they don't contaminate the real-life that they are watching, but then the person sort of hears a small sou

Or what about: the photographer tries to hide so that they don't contaminate the real-life that they are watching, but then the person sort of hears a small sound from the photographer's direction -- they don't actually SEE the photographer, but they get interrupted. Or: the CCTV is well hidden, but the people who installed it left behind some mud that got on someone's shoes and that made them late...