patrick.net

https://patrick.net/post/1340400/2021-08-01-why-printers-add-secret-tracking-dots

Big Brother is watching you.

I actually had that idea on my own - I didnt know it actually existed.

I came up with the idea after thinking about how I bet all pictures I take on my phone likely do the same thing - encode some info into the photo itself (not the text meta data where they store gps). They would need to be slick so as to make sure the encoded data survives typical jpg and png compression, but I bet they can do that and be successful on most images if they design the encoding scheme with those compression algos in mind.

Steganography.

Yep. Hiding data within other data. There's software that will allow you to do this as well. OpenStego, for instance.

This was also used in Blu-Ray copy protection, known as Cinavia. They encoded a watermark into the audio stream which was undetectable to human ears, but the players could detect its presence. If you played a disc that contained such a marked audio stream and the player knows the disc is a BD-R and not a pressed disc, it will halt playback.

It was quite a durable transform as well. If you didn't know exactly what was hidden in the stream, and sought to destroy it by re-encoding, down-sampling, or distorting the audio, you'd find that you had to degrade the quality so badly before the protection was no longer detectable, that it was no longer worthy of the source you copied it from.