An article in today’s London Free Press by David Canton of eLegal talks about the concern the European Commission for Justice, Freedom and Security has about tracking dots that some colour laser printers leave on printed material. From David’s article:
Printer makers are able to encode the serial number, manufacturing code and the date of printing through a series of small yellow dots interspersed on the printed paper. These dots are invisible to the naked eye…
Xerox has admitted it provided tracking dots to [the U.S.] government. At present, only select enforcement agencies have the capacity to read the codes. Though the agencies insist they only use the information gleaned for criminal counterfeit investigations, there are no laws to stop government from abusing the information.
As David points out, the Electronic Frontier Foundation has lots of material on this, including a list of printers that they were able to determine did in fact use tracking dots.
I should think that law firms should at least know whether their printers are marking up documents with invisible characters, in the same way that they should know about the metadata that Word and other word processors embed in a document.