tl;dr your computer display and/or cable act as a transmitting antenna, and indeed you can see the contents of someone's screen by listening in on the right frequency; this software hopes to prevent that
This software implements the "everything is random except most significant bit of green channel" countermeasure against Van Eck phreaking described in . It can display text and images (grayscale).
 Kuhn, M. G. Electromagnetic eavesdropping risks of flat-panel displays. Proceedings of the 4th international conference on Privacy Enhancing Technologies. 2004, pp. 88-107.