On: Primg – Generate prime numbers whose binary repres...

[redfast00]

No, not really: if you take a picture of something, it won't have the exact same pixel values every time you take it. A QR code would be way easier.

[ars → redfast00]

It's scaled to 32x32 black and white. The pixel values don't have to be that similar, only reasonable close.

[progval → ars]

But that's only 1024 bits, assuming values of each pixel is independant from its neighbors. Which it isn't, so you are well under 1024 bits.

[Cyberdog → ars]

But then I'm guessing it fudges pixels/bits until it ends up with a prime number. Is that fudging deterministic, or just random?

[progval → Cyberdog]

It tests primality of numbers greater than the number corresponding to the input image by incrementing. So it's deterministic.

[esnard → progval]

Actually it's decrementing: https://github.com/geonnave/primg/blob/master/index.html#L82

I guess it could change the whole image if the last pixels are "000...000", which happens when the top-left corner has an opposite color to the bottom-right one.

This image can't be "primed" correctly, for example: https://i.imgur.com/ms3sXtF.png

[Cyberdog → progval]

Incrementing… So pixels at the bottom right of the image are the most likely to be flipped from the source image. Interesting. (Edit: Assuming big-endianness and left-to-right, top-to-bottom printing of the pixels/bits)

Nonetheless, yes, using this to create security keys would probably be a good way to lose your bitcoin. :D

[ars → Cyberdog]

Clearly the current implementation is not enough, but I wonder if there is a way to do this properly with actual security, and yet be reproducible for a normal human (we can assume the same camera and lighting).

Maybe some kind of marker in the image that is used for cropping and scaling?

Being able to see a particular image, and at a particular time of day (or indoors I guess), would definitely be an interesting security key.

(Hollywood: feel free to take this idea and do it badly :)