Many color printers surreptitiously print a stegonographic watermark with yellow dots to make all documents traceable to their source. Some threads covering this:

• (law) https://lemmy.sdf.org/post/45605675
• (boycott call) https://lemmy.sdf.org/post/45608582
• (asshole design) https://lemmy.sdf.org/post/45653037

proposal:

In principle, a color printer could be made to print a blank page so that the page only contains the MIC watermark. It could then be scanned at 600+ DPI. A FOSS app could analyze the dot spacing and work out where to add dots to the uniform grid and produce a mask that can be easily layered on to all documents using ImageMagick.