Is is possible to embed metadata in an analog print?
Not only is it possible, it's pretty much certain that every page printed by every laser printer available from every major manufacturer prints at least the following information within the printed image:
- Printer model number
- Printer serial number
- Print date and time
This digital watermark is known as a Machine Identification Code (MIC), and has been around for decades. It is also known as a "yellow dot code" because it uses a grid or constellation of yellow dots, which are very difficult to distinguish under normal viewing conditions. The dots encode around 64 bytes of information within a few square centimeters, and are repeated across a printed page (allowing for information recovery even from a partial printed page). The original purpose of the MIC watermark was to provide a method for government authorities to identify counterfeiters who used increasingly available and inexpensive printers to print funny money. Xerox researched, developed, and patented the technology.
From this Electronic Frontier Foundation (EFF) list of laser printers known to employ some sort of tracking code (whether by yellow dots or other means),
(added 2017) Reminder: It appears likely that all recent commercial color laser printers print some kind of forensic tracking codes, not necessarily using yellow dots. This is true whether or not those codes are visible to the eye and whether or not the printer models are listed here. This also includes the printers that are listed here as not producing yellow dots.
(Note that the list is no longer being updated, as it is assumed that all color laser printers use some sort of forensic tracking codes).
The investigation and arrest of Reality Winner for her 2017 NSA leak was reported to have been enabled by the use of MIC printer codes. The codes probably weren't necessary (enough other forensic information was more readily available (IT logs)), but some of the specific details of the printed document's code has been reported.