There actually is a way of insert codes into picture/video...
I had read about this too - but figured it was some sort of computer code hidden in the mass of “0101110”s forming an image that could somehow be picked apart.
I kinda figured it wasn’t some guy holding up a sign in the mirror during the shower scene, or some gal breathlessly talking in code: “Do it like you did in Syracuse...”
Hmmm - not porn related (I don’t think!) - but my Dad would write my mom letters in code to let her know where he was (WWII). They had names of cities for the various islands, and then he would write things like “I hope your brother’s new job in Chicago goes well...”