
EURion constellation - curtis
https://en.wikipedia.org/wiki/EURion_constellation
======
hatsunearu
Here's one more thing that is used to track counterfeit currency and other
purposes: secret tracking dots on printers.

[https://www.youtube.com/watch?v=sit6zUQKpJc](https://www.youtube.com/watch?v=sit6zUQKpJc)

[https://www.eff.org/pages/list-printers-which-do-or-do-
not-d...](https://www.eff.org/pages/list-printers-which-do-or-do-not-display-
tracking-dots)

~~~
gherkin0
Couldn't that be defeated by a preprocessing step that inserts yellow dots at
every grid position on the printout? If the extra dots were aligned correctly,
I don't see how someone could recover the encoded information.

Someone could probably create a printer driver that does that automatically.
It probably would need some calibration to work, though.

~~~
schoen
I was briefly trying to do that as part of our project about this but I didn't
figure out the proper pixel size and offset, nor whether you can use a fixed
offset relative to the edge of the page or whether the printer tries to defeat
this by slightly randomizing the offsets. I hope someone will figure it out.

There's an additional challenge that some more recent printers often use a
different watermarking technique whose details have never been documented.

------
Legogris
Privacy-minded people could print this on a t-shirt.

~~~
wiml
I've always wanted to incorporate it into a mural or graffiti. Or car paint.

There's a Gibson novel, I think, where the protagonist at some point obtains
t-shirts with a pattern which is recognized by the universal DRM-enforcement
code in video camera chipsets, making them invisible to surveillance.

~~~
jaxb
yes, that's Gibson's "Pattern Recognition".

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DanBC
This website talks about software detection of currency (and it's well worth a
read):
[http://www.cl.cam.ac.uk/~sjm217/projects/currency/](http://www.cl.cam.ac.uk/~sjm217/projects/currency/)

And here's a thread about it:
[https://news.ycombinator.com/item?id=7006848](https://news.ycombinator.com/item?id=7006848)

Here's a thread about a BBC article:
[https://news.ycombinator.com/item?id=9776985](https://news.ycombinator.com/item?id=9776985)

------
bri3d
Interesting, previous HN thread about money anti-counterfeiting, including
EURion:
[https://news.ycombinator.com/item?id=9314523](https://news.ycombinator.com/item?id=9314523)

------
Ezhik
That's interesting stuff. I wonder how the algorithms work, they have to be
pretty fast if they're running on the printer itself.

Also, slightly unrelated, but this for some reason reminded me of a certain
issue some copiers had a while back, where they would swap certain
numbers/letters for some reason when copying. Don't really remember what the
cause of that was, though.

~~~
tajen
The reasonable reason was compression. Parts of the image which looked alike
were saved in the same buffer, that meant especially numbers. Which is the
right way to lose the trust from your customers.

~~~
wiml
It is an interesting observation about compression loss though. The more
sophisticated any compressor gets, the more its artifacts are going to look
semantically plausible.

With simple technology, at first, you might get grainy or blurry images, or
poor frequency response in audio. Those are easy to perceive as artifacts of
the medium. Then you get things like JPEG fringes and context-dependent color
shifts, which are a bit harder to learn to see past, since they are
interacting with the image in sophisticated ways. JBIG (from the article)
detects and compresses repeated textural elements or multiply-used glyphs, but
if it applies that behavior to something that is actually information-bearing,
it'll produce convincingly misleading artifacts.

There's a sequence in _A Fire upon the Deep_ where two people are conversing
over a link with rapidly deteriorating bandwidth— their communicators are
compressing more and more heavily to compensate, until at the end the
character is "interacting" with a sophisticated Markov-like model of their
interlocutor with only a few bits per second of actual entropy from the far
end. Or possibly none at all.

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tgsovlerkhgsel
Desktop software and modern printers/scanners no longer use this, they use
something based on watermarking. I suspect it may have something to do with
the fine pattern of parallel lines, which you will find on almost every
currency.

I suspect this patent might have something to do with it, but the math is
beyond my comprehension:
[http://www.google.com/patents/US7720249](http://www.google.com/patents/US7720249)

This patent was referenced by the above patent and seems even more applicable:
[http://www.google.com/patents/US6449377](http://www.google.com/patents/US6449377)
(references patents 5583614, 4723149, 5633952, 5640467, and 5424807 which may
be good further reading).

I also remember someone mentioning that they reverse engineered the currency
detector code in Photoshop(?) and got something like "fourier mellin
transform, followed by checking specific values in an array".

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hackuser
Does open source software include this code? Does anyone know of examples?

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bpicolo
I was actually always curious as to why Adobe would go out of their way to add
bank note detection. Now I know they didn't, some outside entity did it for
them! Cool.

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larsboehnke
interesting, thanks

