Take any page you've printed on a color laser printer and look at it under a blue LED or UV light. If you look closely enough at a blank area of the page, you'll see a faint pattern of tiny yellow dots — arranged in a precise grid, almost too small to see with the naked eye. They're on every page. They've been there for decades. And most people have no idea.
This is one of the most widespread, real-world examples of steganography in existence — hiding information in plain sight on hundreds of millions of documents, completely without the knowledge of the people printing them.
Printer tracking dots — formally called Machine Identification Codes (MIC) — are a system where color laser printers embed a unique, invisible watermark on every page they produce. The dots encode the printer's serial number, and often the date and time of printing.
The dots are printed in yellow — the color least visible to the human eye on white paper. They're small enough that most people will never notice them without magnification. But under a blue light (which makes yellow fluorescent and highly visible) or with a high-resolution scan and image processing, the pattern becomes clear.
The technology dates back to the late 1980s, when color laser printers first became capable enough to produce convincing counterfeit currency. The U.S. Secret Service and other government agencies reached agreements with printer manufacturers — Xerox, Canon, HP, and others — to embed identifying information in every printout. The goal was to make it possible to trace counterfeit bills back to the printer that produced them.
The arrangement was largely secret for years. The public became aware of it in 2004 when the Dutch research group Bits of Freedom published findings about the dots. In 2005, the Electronic Frontier Foundation (EFF) confirmed the existence of the system after decoding tracking dots from multiple printer manufacturers. The EFF published a chart showing the dot patterns from various printers and how to decode them.
The exact encoding varies by manufacturer, but typically includes:
Some patterns may also include the manufacturer's model code. The serial number is the key piece — it can be traced back to the specific unit, which was sold to a specific retailer, which may have records of who purchased it.
The short answer: most color laser printers from major manufacturers. Xerox, Canon, HP, Brother, Ricoh, and others all implement some form of machine identification code. Inkjet printers generally do not use the same yellow dot system, though some may have other forms of watermarking.
Black-and-white laser printers cannot print yellow dots (they have no yellow ink), so they're not affected. The system is specific to color laser printing.
The EFF maintains a database of printer models and whether they're known to embed tracking codes, though the list hasn't been comprehensively updated in recent years.
In most countries, yes — at least for the manufacturers. The implementation was done at the request of governments under agreements with printer companies, and there's no law requiring manufacturers to disclose the practice to consumers. In the United States, there's no legal requirement that your printer tell you it's watermarking your documents.
Whether it's a good policy is a different question. Privacy advocates have raised concerns about the chilling effect on legitimate anonymous speech and whistleblowing — if any document printed on a color laser printer can potentially be traced to its source, it meaningfully limits the practical ability to print and distribute anonymous materials, even for entirely lawful purposes.
Printer tracking dots are a remarkable example of steganography deployed at massive scale — billions of pages, silently watermarked, for decades, without public knowledge or disclosure. It demonstrates how invisible information can be embedded in physical media just as effectively as in digital images.
The technique is essentially the same as digital LSB steganography, just implemented in the physical domain: tiny modifications that are imperceptible under normal conditions but detectable with the right analysis. The principle is identical. The scale is extraordinary.
If you're interested in how digital image steganography works, the same principles apply. Our steganography explainer covers LSB encoding in detail, and our steganography history article puts printer tracking dots alongside other historical examples of hidden messages.
Hide a secret message inside a PNG image using the same LSB principle printers use to hide tracking dots. Runs in your browser — nothing is uploaded.
Open Steganography Tool