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Behind the yellow dot of the printer: How did it help track criminals?
The yellow dot of the printer, namely the printer steganography or machine identification code (MIC), is a digital watermark that many color laser printers and photocopiers generate when printing on each page, identifying the documents printed using the device.The existence of the Yellow Dot was not known to the public until 2004 since its development by Xerox and Canon in the mid-1980s.The original intention of this technology is to prevent its color copiers from being used to counterfeit banknotes.
This secret tracking code is intended to eliminate concerns that its color copiers may be used to counterfeit banknotes.
In the mid-1980s, Xerox pioneered a coding mechanism that distributes a unique number in tiny dots throughout the printing area.This system was first used in its DocuColor series printers and obtained a US patent.Over time, this solution has been widely deployed in printers from other manufacturers, and many printers have begun to use these yellow dots to identify the source of the document.
In October 2004, Dutch authorities used tracking codes to track suspects for the first time, using a Canon color laser printer.As the incident was exposed, the public gradually learned about the existence of machine identification codes.This technology not only helps law enforcement agencies track fakers, but also reveals the opacity of some agencies when conducting surveillance activities.
All the manufacturers of major color laser printers appear to have reached a secret agreement with the government to ensure that the output of such printers is forensic traceability.
In terms of technology, the yellow dots have a diameter of about 0.1 mm and a distance of about 1 mm, and their arrangement encodes the serial number of the device, the date of printing and the time of the print.This arrangement can appear in the printing area multiple times.If errors occur, these yellow dots can still be analyzed and can even be further observed through a microscope.Scientists' research on this technology shows that early printers could store up to 64 bytes of data.
Although these yellow dots are usually nearly invisible, it is very likely to be seen with a magnifying glass in good lighting conditions.And under UV light, these yellow dots are more conspicuous.The application of this steganography means that even copy or shredded documents can be identified afterwards, such as in the 2011 DARPA’s “Smasher Challenge”, a team showed How to rebuild broken files.
The codes left by these printers can be located in different parts of the paper, and can still be identified even if the file is corrupted.
In practical applications, some journalists and security experts pointed out that when the "Intercept" website handled leaked documents by the face-seeker Reality Winner, it was unmodified to publish secret NSA documents including printer tracking points, which led to Winner being identified. And was arrested in 2017.This incident reiterates how to leave traces for tracking when using a printer, and has caused many people to rethink her and our privacy protection.
We do not know that the data will be accidentally leaked with photocopy or printed copies, which is unaware of by many users.
It should be pointed out that although many users are not aware of the existence of these yellow dots, they can reveal user's personal information, such as health status, bank account details, etc.In 2005, the Electronic Frontier Foundation (EFF) attempted to find a decoding method and released a Python script for analyzing these points.Until 2018, scientists at the Technical University of Dresden developed and released tools specifically for extracting and analyzing these steganography to assist whistleblowers in solving problems.
With the advancement of technology, manufacturers may also adopt other less obvious identification methods, which makes it urgent to find more effective privacy protection measures.So, can our digital privacy continue to be threatened without being discovered?
