I got this on the ZX Spectrum, and it came with one of those plastic converters. There would be a code on the screen and you had to put the plastic thing in front of it to decode the image and type in the letters. To stop people from pirating the game by making a tape to tape copy of it.
(Of note: 3D printers still can't print Lenslok type devices; This is perhaps the only form of copy protection from those days that is still not trivially breakable)
