To obtain the largest benefit from photo enforcement systems, law enforcement agencies must consider the equipment and its applications. Standards must be developed for its use, and storage policies for the images must be established. A photograph usually is admissible as evidence under the "pictorial testimony theory." The photograph must be accompanied by an officer or other authorized individual who was present at the time the photo was taken to attest to the photograph's validity. To meet this requirement, the Mesa Police Department (Arizona) positions a uniformed officer in every speed enforcement van. In many cases, however, officers or duly authorized individuals are not present at speed or red-light enforcement locations. Under such conditions, the theory of "silent witness" applies. Under this theory, photographs constitute "substantive evidence" by drawing admissibility from the reliability and verification of the photographic process used. Any agency considering photo enforcement should check with local and State authorities to determine whether the "silent witness" theory applies in its jurisdiction. More importantly, with the relative ease of altering photographs, jurisdictions that are considering photo enforcement must guarantee the security of the photographic evidence. A chain of custody must be established for the evidence to ensure fair prosecution. An agency should obtain an assurance from the equipment vendor that a representative is available to testify about the device's triggering and camera operation procedure. It should determine the availability of testimony about the device's service history. Mechanisms must be in place to prove only authorized individuals had access to the camera system. An agency should also maintain a custody transfer record for each canister of film, cassette, or video evidence. Before implementing photo enforcement, an agency should conduct an aggressive and pervasive public information campaign to inform the public about the program's implementation and benefits.