The whole issue seems to be dedicated to watermarking, but relevant to this discussion is also this article: "The basic principle borrows from spread spectrum

The whole issue seems to be dedicated to watermarking, but relevant to this discussion is also this article: "The basic principle borrows from spread spectrum communications. It consists of addition of an encrypted, pseudo-noise signal to the video that is invisible, statistically unobtrusive, and robust against manipulations." https://www.sciencedirect.com/science/article/pii/S0165168498000115 https://www.sciencedirect.com/science/article/pii/S016516849...