Printer tracking dots

In the mid-1980s, Xerox pioneered an encoding mechanism for a unique number represented by tiny dots spread over the entire print area, and first deployed this scheme in its DocuColor line of printers.

Xerox developed this surreptitious tracking code "to assuage fears that their color copiers could be used to counterfeit bills"[1] and received U.S. Patent No.

[4] In November 2004, PC World reported the machine identification code had been used for decades in some printers, allowing law enforcement to identify and track counterfeiters.

[2] In 2005, the civil liberties activist group Electronic Frontier Foundation (EFF) encouraged the public to send in sample printouts and subsequently decoded the pattern.

According to the Chaos Computer Club in 2005, color printers leave the code in a matrix of 32 × 16 dots and thus can store 64 bytes of data (64×8).

"[10] In 2018, scientists at the TU Dresden analyzed the patterns of 106 printer models from 18 manufacturers and found four different encoding schemes.

[11] The dots 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 the dots of the identification code clearly visible.

In 2005, the Electronic Frontier Foundation (EFF) sought a decoding method and made available a Python script for analysis.