Machine Identification Code
A Machine Identification Code (MIC), also known as printer steganography, yellow dots, tracking dots or secret dots, is a digital watermark which certain color laser printers and copiers leave on every single printed page, allowing to identify the device with which a document was printed and giving clues to the originator. Developed by Xerox and Canon in the mid-1980s, its existence became public only in 2004. In 2018, scientists developed privacy software to anonymize prints in order to support whistleblowers publishing their work.
In the mid-1980s Xerox pioneered an encoding mechanism for a unique number represented by tiny dots spread over the entire print area. Xerox developed the machine identification code "to assuage fears, that their color copiers could be used to counterfeit bills"  and received U.S. Patent No 5515451 describing the use of the yellow dots to identify the source of a copied or printed document.
In November 2004, PC World broke the news that this machine identification code had been used for decades in some printers, allowing "law enforcement to identify and track down counterfeiters". The Central Bank Counterfeit Deterrence Group (CBCDG) has denied that it developed the feature.
In 2005, the civil rights group Electronic Frontier Foundation (EFF) encouraged the public to send in sample printouts and subsequently decoded the pattern. The pattern has been demonstrated on a wide range of printers from different manufacturers and models. The EFF stated in 2015 that "the documents that we previously received through FOIA suggested that all major manufacturers of color laser printers entered a secret agreement with governments to ensure that the output of those printers is forensically traceable. [...] it is probably safest to assume that all modern color laser printers do include some form of tracking information that associates documents with the printer's serial number."
In 2007, the European Parliament was asked about the question of invasion of privacy, since a color print bears the unique fingerprint of a laser printer, and allows tracking the buyer and owner especially when paid for electronically.
The pattern consists of a dot-matrix spread of yellow dots, which can barely be seen with the naked eye. The dots have a diameter of a tenth of a millimeter (0.004") and a spacing of about one millimeter (0.039"). Their arrangement encodes the serial number of the device, date and time of the printing, and is repeated several times across the printing area in case of errors. For example, if the code consists of 8 × 16 dots in a square or hexagonal pattern, it spreads over a surface of about 4 square centimetres (0.62 sq in) and appears on a sheet of size DIN-A4 paper about 150 times. Thus, it can be analyzed even if only fragments or excerpts are available. Some printers arrange yellow dots in seemingly random point clouds.
As of 2011[update], Xerox was one of the few manufacturers to draw attention to the marked pages, stating in a product description, "The digital color printing system is equipped with an anti-counterfeit identification and banknote recognition system according to the requirements of numerous governments. Each copy shall be marked with a label which, if necessary, allows identification of the printing system with which it was created. This code is not visible under normal conditions."
The Machine Identification Code can be made visible by printing or copying a page and subsequently scanning a small section with a high-resolution scanner. The yellow color channel can then be enhanced with an image processing program, to make any dots of the MIC clearly visible. Under good lighting conditions, a magnifying glass may be enough to see the pattern. Under UV-light the yellow dots are clearly recognizable.
Using this steganographic process, high-quality copies of an original (e.g. a bank note) under blue light can be made identifiable. Using this process even shredded prints can be restored: The 2011 "Shredder Challenge" initiated by the DARPA was solved by a team called "All Your Shreds Are Belong To U.S." consisting of Otavio Good and two colleagues.
Protection of privacy and circumvention
Copies or printouts of documents with confidential personal information, for example health care information, account statements, tax declaration or balance sheets, can be traced to the owner of the printer and the creation date of the documents can be revealed. This traceability is unknown to many users and inaccessible, as manufacturers do not publicize the code that produces these patterns. It is unclear which data may be unintentionally passed on with a copy or printout. In particular, there are no mentions of the technique in the support materials of most affected printers (exceptions see below). In 2005 Electronic Frontier Foundation (EFF) sought a decoding method and made available a python script for analysis.
In 2018, scientists from the TU Dresden developed and published a tool to extract and analyze the steganographic codes of a given color printer and subsequently to anonymize prints from that printer. The anonymization works by printing additional yellow dots on top of the Machine Identification Code. The scientists made the software available in order to support whistleblowers in their efforts to publicize grievances.
Other methods of identification are not as easily recognizable as yellow dots. For example, a modulation of laser intensity and a variation of shades of grey in texts are already feasible. As of 2006[update], it was unknown whether manufacturers were using these techniques.
- EURion constellation, a dot matrix spread over a bank note, which stops some printers and color copiers from processing.
- deda on GitHub
- Richter, Timo; Escher, Stephan; Schönfeld, Dagmar; Strufe, Thorsten (2018-06-14). "Forensic Analysis and Anonymisation of Printed Documents". Proceedings of the 6th ACM Workshop on Information Hiding and Multimedia Security. ACM: 127–138. doi:10.1145/3206004.3206019. ISBN 9781450356251.
- "Dresdner Forscher überlisten Tracking-Punkte bei Laserdruckern". heise online (in German). 25 June 2018.
- Jason Tuohey. "Government Uses Color Laser Printer Technology to Track Documents". PC World. 22 November 2004.
- Stephan Escher Tracking Dots unlesbar machen. Interview mit Uli Blumenthal Deutschlandfunk. 28 June 2018 (in German)
- Wilbert de Vries. "Dutch track counterfeits via printer serial numbers". PC World. 26 October 2004.
- "DocuColor Tracking Dot Decoding Guide". Electronic Frontier Foundation. 2005. Archived from the original on 5 March 2018. Retrieved 5 July 2018.
- "Electronic Frontier Foundation". Electronic Frontier Foundation.
- Lee, Robert (2005-07-27). "Freedom of Information Act (FOIA) request" (PDF) (Letter). Letter to Latita M. Huff. Electronic Frontier Foundation. Retrieved 2016-11-07.
- "List of Printers Which Do or Do Not Display Tracking Dots". Electronic Frontier Foundation. Retrieved 11 March 2011.
- European Parliament Tracking codes in photocopiers and colour laser printers Parliamentary questions. 20 November 2007.
- Frank Rosengart (2005). "Datenspur Papier". Die Datenschleuder, Das wissenschaftliche Fachblatt für Datenreisende [technical factsheet] (PDF). Hamburg: Chaos Computer Club. pp. 19–21. ISSN 0930-1054. Retrieved 2011-02-27.
- "Abschnitt „Technische Daten des Digitalen Farbdrucksystems Xerox DocuColor 6060"". Xerox DocuColor® 6060 Digitales Farbdrucksystem (PDF; 1,4 MB) (Prospectus). Neuss: Xerox GmbH. p. 8. Retrieved 2011-02-27.
- "Beitrag bei Druckerchannel: Big Brother is watching you: Code bei Farblasern entschlüsselt". Druckerchannel.de.
- "CONGRATULATIONS to "All Your Shreds Are Belong To U.S."!". Defense Advanced Research Projects Agency. 2011-11-21. Retrieved 2014-06-12.
- "Tip for Bad Guys: Burn, Don't Shred". Bloomberg Businessweek. 2011-12-15. Retrieved 2014-06-12.
- "docucolor.cgi - CGI script to interpret Xerox DocuColor forensic dot pattern". Electronic Frontier Foundation. 2005. Archived from the original on 2017-05-08. Retrieved 2018-10-03.
- So verpfeift dich dein Drucker nicht 26 June 2018. Deutschlandfunk Nova (in German)
- Printer Characterization and Signature Embedding for Security and Forensic Applications Pei-Ju Chiang, Aravind K. Mikkilineni, Sungjoo Suh, Jan P. Allebach, George T.-C. Chiu, Edward J. Delp., Purdue University, 2006 (poster)