US Patent 8648911 Communication system, control device, and reception device

A control device divides one frame into plural sub-frames, distributes image signals of an embedded image, which is provided to only specific users, to the plural sub-frames such that a sum of signal levels in the one frame is zero, and superimposes the image signals on an image signal of a basic image provided to unspecified people and causes a display device to display the embedded image. The reception device shoots an image displayed on the display device in each period that is the same as the period of the sub-frame and calculates the difference between two image signals obtained in each period that is the same as the period of the sub-frame to acquire and display an image signal of the embedded image.