In Omaha, red-light cameras are required to take two pictures of you(on the same film, as I read it). One with you before you enter the intersection, one with you in the intersection. Both pics must show that the light is red. These cameras have been placed at high-traffic intersections. Surrounding traffic/lighting/etc doesn't change that much between before you enter and when you're in the intersection. Thus the city and the police both have proof that you entered when the light was red.