From Quake Wiki
He took the screenshots on the back of the Quake box. "those are my screenshots on the package :)"
2015-05-28, "Meet John Romero: One of the Godfathers of the First-Person Shooter" by Motherboard: https://www.youtube.com/watch?v=9v_0HD7iOz4
- John Romero on Twitter, 28 July 2015 https://twitter.com/romero/status/626018996450631680