Marker system, to give detection or interference of illegal filming at public events, uses a light spectrum invisible to the human eye which triggers an electronic response

摘要

The system for the detection of optical signals invisible to the human eye, e.g. illegal filming at public events, uses markers which register one or more marker signals. The markers are electronic and are structured to respond to given types of signals. At least one marker signal is in the infra red spectrum. At the venue, e.g. a cinema auditorium (12), the film is shown from a projector (16) at the screen (14). An invisible optical signal (22) is sent from a marker unit (10) to the screen, and reflected (18) back to the audience seats (20) to detect any emissions from the audience.