When video content is watermarked, typically during encoding (but also potentially at time of individual device delivery or even during specific device playback), it means that some form of individualized identifier information (often termed a payload) is added to the main video content. The identifier payload is - by design - intended to be subliminal or imperceptible, so that it does not interfere with the viewing experience. But because the payload and the video are combined on the screen, any capture or copy made will also include that payload. When an illegal copy of a video is re-distributed, the payload can be extracted and acts as a way to trace the source of that copy to provide an additional form of security mechanism that extends beyond the envelope of encrypted delivery. For more general information on video watermarking please refer to the Digital Watermarking Alliance http://digitalwatermarkingalliance.org/