Your office color laser printer adds yellow dots, too small for the average person to see, to every page. The dots form patterns which identify the printer make and model. Printer companies, at the request of the U.S. government, have added the dots as a way to trace documents back to the printer. The Electronic Freedom Foundation, an organization concerned with civil rights and technology, has investigated the use and nature of these yellow dots.

Information Printed The yellow identifying dots produced by color laser printers carry information identifying the printer's make, model and serial number. If the printer has the current date and time, the dots identify that as well. Only the printer manufacturers and the government know the exact information contained in the dot patterns, although outside investigators have partly deciphered its meaning.

Affect on Documents The yellow color has very low contrast against white paper, making the dots hard to detect with the naked eye. The laser printing mechanism itself generates the dots. Under most circumstances, the dots do not compromise the quality of photos, graphics or other documents produced on laser printers. Because the dots are small, they likewise have little effect on toner consumption.

Purpose As the resolution of color copiers and laser printers has improved, the technology has simplified money counterfeiting and other types of forgery, which is why the FBI and the U.S. Secret Service have asked equipment makers to develop a method where law enforcement can detect counterfeit money produced on these machines, and then trace the currency back to the source.

Types of Printers Affected The yellow dot technology appears to apply only to color laser printers and copiers. Monochrome laser, LED and inkjet printers lack the yellow toner necessary to print the dots, and therefore do not produce these markings. In addition, because Xerox developed the yellow dot technology during the 1990s, this affects only those printers made since then. Experts have identified yellow dot marks on documents from many printer makes, including Xerox, Hewlett-Packard, Toshiba and Canon. At the time of publication, experts know of no other secret identifying marks in printed materials, although the possibility exists, according to the Electronic Freedom Foundation.

Making Dots Visible You can increase the contrast of the yellow dots by shining a strong blue light on a printed document. Light from a blue LED "keychain" source, for example, makes the yellow dots appear black, making them easier to see. A page with little content makes a good candidate, as the black dots stand out better against a blank background.

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