eff.org

J0AQ TIL that many printers print barely visible dots on every page which allow the printed pages to be forensically traced. Most, if not all, major printer manufacturers have a secret agreement with the government to ensure the documents can be accurately traced.
w1VY TIL many color laser printers employ ‘hidden’ dot codes that encode the serial number of the specific printer on every printed page to make your documents forensically tracecable back to the printer. The EFF believes printer manufacturers agreed in secret with governments to provide this tracking.
rVxw TIL printers from Canon, Xerox, others add nearly-invisible dots to each printed page containing encoded print date and serial number of printer