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.
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.
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.
If refusing to process/print Eurion marked things was a legally required feature (which it currently isn't) in printers/image processing software, it could pose quite a conundrum for OSS, if the law also requires that the feature not be easily disabled by an end user. It's hard for me to imagine OSS software with this property. Yet the law could demand it, and society might find it reasonable.
Unfortunately, imaging systems co-evolved with humans, thus they tend to hack things so that they are sensitive to light in the exact way the human eye is. (Your monitor isn't emitting orange light, it's fooling your eyes by making it think the light is orange by activating red/green/blue-sensitive chemicals in your eyes the same way orange things do.)
Digital cameras can be pretty sensitive to IR, but there is typically an IR filter over the sensor to prevent detection.
One cool trick I learned was how you can take a normal remote control and view the IR light flashing when looking at it through your mobile phone camera. It's useful for determining if the batteries are still good in the remote, for example.
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.
I'd be very interested to know, as it seems to have some interesting properties: can run on limited CPU devices yet easily cope with high resolution images, in a range of colours and contrasts, and and can detect the pattern at a range of sizes and orientations.
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.
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.
I've run into this with cell-phones too. Someone was reading an alphanumeric value to me, and one letter reliably sounded like one number. It was really odd, but apparently some of the compression techniques for phones use speech models and it seems that the person on the other end had an accent that hit a poor spot in the model.
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.
This patent was referenced by the above patent and seems even more applicable:
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".
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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https://www.youtube.com/watch?v=sit6zUQKpJc
https://www.eff.org/pages/list-printers-which-do-or-do-not-d...