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Comment by monopolemagnet | Hacker News Reader

This has been known for over a decade.

https://en.wikipedia.org/wiki/Printer_steganography

Anything printed on most (but not all) color printer can be traced back to the printer on which it was printed (serial number) and often date stamp as well.

https://www.eff.org/pages/list-printers-which-do-or-do-not-d...

Furthermore, most image editing programs and many scanners and copiers often refuse to capture currency because of microprinted circles.

https://freedom-to-tinker.com/blog/felten/photoshop-and-curr...

http://www.cl.cam.ac.uk/~mgk25/eurion.pdf

http://www.rulesforuse.org/pub/index.php?lang=en

(note: official US currency images have link-rotted away)

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The EURion pattern, with the circles, isn't exactly "microprinting" -- you can see it quite clearly without magnification on a lot of currencies. But there is also the later Digimarc system, and we don't know exactly how it works. Maybe somebody will reverse engineer the detection software.

Edit: as I noted on the list of printers page, we think that newer printers are also doing something that we can't see, possibly based on perturbing dithering algorithms so that the dithering is different from printer to printer in a distinctive way. So when we didn't see yellow dots from newer printers, that doesn't necessarily mean that they aren't printing tracking codes. The reasons for thinking that tracking codes became more pervasive in newer printer models rather than being phased out are suggestions in documents obtained via FOIA, and rumors from people who worked in the industry.

Sounds like it is time to buy a printer, rip it apart and document the firmware after reverse assembling it.

"Reverse assembling" == "disassembling"

Reverse engineer, apologies. The idea is to gain understanding, not simply to get a disassembly (that's an automated process and a 1:1 correspondence between binary and assembly code remains).

The harder part is to figure out what it all does.

I wonder whether any over-zealous publishers started to put EURion constellations in their books in order to deter photocopying and scanning.

The rings would be cool to hijack for watermarking, but they look really fussy.

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