"most printers print special patterns of "invisible" dots on every sheet printed" I believe this is only relevant to color printers since black pixels would be

"most printers print special patterns of "invisible" dots on every sheet printed" I believe this is only relevant to color printers since black pixels would be noticeable. Additionally if you were to copy/scan the document (even in color) you could alter the imaging to yield no yellow dots by exposure or contrast settings (this is common in the printing industry). Also, this assumes that the serial number of the printer is registered. While it would be possible with an extensive search to locate the buyer of a particular printer even if they didn't register the machine (by tracing to a particular dealer etc.) unless you were committing a major crime (like counterfeiting for example) this doesn't seem like something worth the effort or practical in most cases. You could also alter the printer to add additional yellow dots to confuse any interpretation. http://w2.eff.org/Privacy/printers/docucolor/ http://w2.eff.org/Privacy/printers/docucolor/