German researchers defeat printers' doc-tracking dots

Beating the unique identifiers that printers can add to documents for security purposes is possible: you just need to add extra dots beyond those that security tools already add. The trick is knowing where to add them.

Anybody can take a scan of the document, and clear “empty” areas in an image editor, but the group's second technique is more sophisticated. After their algorithm identifies the pattern in use, it takes a mask of all possible dot locations in that pattern, and adds extra dots that conform to the layout, but render the code meaningless.