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Comment by teagee | Hacker News Reader

This must result in a non-trivial amount of ink/toner used in the name of security

The last HP Inkjet that I had would go through the Yellow cartridge faster than black, even when printing only Black and White. Which is how I discovered these fun little dots.

They didn't go into too much detail about how the dots are actually printed (what type of ink, how heavy, etc.), but they imply in the article that at least some tracking dots require a UV light to detect.

I'd be curious to know how the dots actually get printed.

And how do they get printed on a monochrome printer like a laser?

I believe, could be very wrong, that its only on color printers and uses the Yellow color to print dots too small to see with the eye.

There are color laser printers.

On a monochrome printer, I guess you can still to steganography by messing with the dithering, I guess? However, since the stated aim of the fingerprinting is to catch money counterfeiters, I guess they are less interested in monochrome.

Are any major banknotes monochrome?

Each layer is, but that's probably more advanced than just "printing a banknote".

That anti feature is absent there. Black instead of yellow dots would be very visible

Error: Secret UV ink is empty. Please contact NSA for a new cartridge.

I'm not sure if normal scanners detect UV light, but that would break a good chunk of their tracking purpose these days if they were not detectable in scans.

Hi, author here! The dots themselves aren't printed with UV ink it's just that the UV light makes it easier to see them due to the yellow ink used.

There were images I sent the magazine of the dots from some magazines I scanned, but they didn't run them. If you scan a page and invert it, the patterns are more legible https://i.imgur.com/x1TXa30.png

The dot patterns are much smaller and more dense than I expected

I don't understand what I'm looking at here.

You should see rows of tightly packed blue dots in repeating patterns - the machine identification codes for a Xerox printer, to be precise. You may have to turn off f.lux to see them

Interesting protip: fluorescent compounds are added to all sorts of things: mouthwash bottles, toothpaste, white paper, laundry detergent, and the “bright” colours of printer ink.

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