The Electronic Frontier Foundation has an interesting document about color laser printers. It seems that all the manufacturers of color laser printers have entered a secret agreement with the government to add invisible or near invisible markers to all documents. These markers include such information as the date and time the document was printed and the serial number of the printer.
The use of embedded information is printed documents or pictures is not new. It has been used at least since WWII, although it usually involved interested parties that were trying to smuggle information hidden in plain sight.
The use of codes in printers is for the purpose of tracking and finding people who created a print. This might be because the document contained plans or a threat. Or it might be to find someone who had printed a classified document and then leaked it, as was the case of a contractor that printed a document at an NSA facility and delivered to a news website in 2017. She had taken a document concerning Russian cyber attacks on U.S. voting software during the last election.
The document included barely visible dots in a pattern that carried information. That information was enough to track the document to the building and then to her.
In the right lighting, the dots become visible information. It is unlikely that all printers use a system that is so easily detected but every modern printer should be assumed to be embedding information of this type.
You are not paranoid enough. Thus ends your security lesson for today.