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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.

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"just" yes, you "just" have to do it every time. and so does everyone else. sadly we live in a society of comfort, where people do not even remove the trackers from links, so why would you expect they add a blur to images...

My point is, it's easier to remove a spymark than a watermark.

.. both of which visibly degrade quality.

Try.

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

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