Hidden data in a swirly rectangle

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John Gray
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Hidden data in a swirly rectangle

Post by John Gray »

Here in England there is talk of some form of Vaccine Passport to show that the bearer has been given the required two Covid-19 vaccination doses (Pfizer or A-Z). This might enable them to travel abroad, or, in England, enter clubs, pubs or restaurants. It could be downloadable to one's smartphone or as a sheet of paper sent to the injectee (?!) on request.
I chose the latter, and thought it would be a Good Thing to do a couple of copies thereof.
I noticed a 3.5cm x 1.8 cm near the top right of the original letter, which seemed composed of regular swirly lines (with nothing visible other than the aforesaid swirly lines, unlike in my screen grab below!)
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Swirly rectangle.jpg
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However, on the copies, this rectangle had changed to show a diagonal "watermark", which I have simulated by magnifying up the original rectangle:
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Swirly rectangle magnified .jpg
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This is the first time I have encountered such a thing, but undoubtedly many other people know all about it!
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John Gray

Venison is quiet deer, and quite dear.

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Leif
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Re: Hidden data in a swirly rectangle

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Leif

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John Gray
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Re: Hidden data in a swirly rectangle

Post by John Gray »

Thanks, Leif - never heard of that before (and it does seem to be an unusual name).
I was thinking of steganography, but that's not exactly the same thing.
John Gray

Venison is quiet deer, and quite dear.

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StuartR
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Re: Hidden data in a swirly rectangle

Post by StuartR »

I think there also used to be a version of this that used an ink that changed its appearance when the very bright light of a photocopier hit it, but I don't remember what that one was called.
StuartR


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kdock
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Re: Hidden data in a swirly rectangle

Post by kdock »

I've seen paper prescriptions that have "copy" or "void" appear when copied. It's rare that a doctor hands you a physical scrip, but when you get one in your feverish hands, you probably won't be able to copy it without some kind of "watermark" appearing on it.

Kim
"Hmm. What does this button do?" Said everyone before being ejected from a car, blown up, or deleting all the data from the mainframe.