Spymarks just seem like another word for <a href="https://en.wikipedia.org/wiki/Steganography" rel="nofollow">https://en.wikipedia.org/wiki/Steganography. On that note, one way we can prevent it is to assert that all our content is byte-for-byte identical with the last known trusted stage of what we have produced (for example: a camera we are certain does not watermark, an image editor we are certain doesn't watermark, an image compressor we are certain can't watermark, etc). One vector that I am particularly concerned about is social media. Most images and videos uploaded to most social media is re-compressed by the target platform. This is a door to tracking that is far too easy for social media platforms to open. They might rationalize it (if discovered/announced) by saying that our memes won't be reposted, images or work stolen, etc... but honestly I'd rather my work be stolen than tracking information inserted in there. Oh, we also have stuff which is way more secure, like time-stamped cryptographic signatures.
The vulnerability of steganography is that is has to pretend that signal is noise. Remove the noise - and the signal is gone. I'm pretty sure that the simplest gaussian blur will remove the spymark from any picture.
Or... add some noise. Just align the last bit of every pixel channel with a random bit sequence - and Bob's your uncle.
I tried both options, and both options visibly* degraded quality while failing to remove my hidden message. Consider that good schemes are already designed to be resilient in the face of lossy image compression, which is a lot more disruptive than the things you suggested.
* the 7-bit quantization + 1-bit noise option not by much, but still, visible
Retro_Dev · · focus · HN ↗
okaleniuk · · focus · HN ↗
Or... add some noise. Just align the last bit of every pixel channel with a random bit sequence - and Bob's your uncle.
pjc50 · · focus · HN ↗
okaleniuk · · focus · HN ↗
minitech · · focus · HN ↗
* the 7-bit quantization + 1-bit noise option not by much, but still, visible