I am not sure if this is the right network to ask this question but it's the closest I could find.
An acquaintance of mine told me that, when he was a kid, they had some kind of content blocking system for VHS. The way that it worked was that it took the VHS signal and masked that with shapes of the content blocking system, thus blocking out offending images.
So in a scene that contained e.g. graphic violence it would put black shapes over the parts of the image that contained the violence.
The purpose was that this would basically "convert" a movie intended for an older audience so that it was watchable by a younger audience.
From what he recalls you would load the system with a VHS and a second media that contained the blocking shapes for this exact movie. He could not recall whether the blocking media was another VHS or some other kind of storage.
This device was probably sold in the 90s in the USA.
I tried googleing for it, but I could not find it.
Has anyone ever heard of something like this?