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https://en.wikipedia.org/wiki/Video_...nvisible_Light

Video Encoded Invisible Light (VEIL) is a technology for encoding low-bandwidth digital data bitstream in video signal, developed by VEIL Interactive Technologies. VEIL is compatible with multiple formats of video signals, including PAL, SECAM, and NTSC. The technology is based on a steganographically encoded data stream in the luminance of the videosignal.

A recent application of VEIL, the VEIL Rights Assertion Mark (VRAM or V-RAM) is a copy-restriction signal that can be used to ask devices to apply DRM technology. This has been seen as analogous to the broadcast flag. It is also known as "CGMS-A plus VEIL" and "broadcast flag on steroids."

There are two versions of VEIL on the market:

VEIL-I, or VEIL 1, has raw speed of 120 bits per second. It is used for unidirectional communication (TV→devices) with simple devices or toys, and to deliver coupons with TV advertising. It manipulates the luminance of the video signal in ways difficult to perceive to human eye

VEIL-II, or VEIL 2, has speed of 7200-bit/s and is one of the technologies of choice for interactive television, as it allows communication with VEIL servers through devices equipped with backchannels.