3 ms·

Is there a way to reliably scrub an image of any possible hidden watermarks that can be created like this?

topherclay 2y ago
Of course. the first image of the blog post shows that you can "paint over" the largely unused area and you don't lose much of your original image. The hidden watermarks make use of this unused area so you can just paint over that area with blank data in order to "scrub" any hidden watermarks.
- forgotusername6 2y ago
  I'm pretty sure you could also layer the cat noise evenly over the image without significantly damaging the woman. The DCT puts all the importantly information top left, but there is nothing stopping you adding a step to distribute that information across the whole image, or using another transform that didn't have the same concentration effect
  - topherclay 2y ago
    Well sure, but whatever extra step you use to encode you will also need as an extra step to decode.
tsukikage 2y ago
"Reliably" is a difficult word. If you understand how a specific watermark works, then yes, absolutely. If you want a fully general method that counters every possible thing you might come across... well. That's hard. "Imperceptible" watermarks work by altering detail humans don't notice or pay attention to. So your scrubber would need to reliably remove or change all such detail. Removing such detail is absolutely something we can do - the article mentions one way, other commenters make other suggestions, and also lossy image compression in general works by losing exactly such details from the compressed image so there's that as well. But /reliably/ get rid of /everything/, so you can be /completely certain/ no watermarks encoded in ways imperceptible to a human can possibly be left, without knowledge of the specific watermarks you want to remove or at least a way to test for their presence? You're looking at some drastic technique, in the realm of "theoretically possible but impractical"; e.g. one way might be to hand the image to a human artist, commission them to paint a copy, scan that in and use that. Note how, in the article, it's still possible to pick out the cat even as the jpeg compression level increases. If someone found a way to avoid encoding that information without degrading original image in ways noticeable to human observers, we'd all be all over that, because it would give us a way to make image files even smaller than we can now. This is an active area of research, precisely because it is key to getting better compression for sound and video to better understand how humans perceive things, what they notice and what they do not, so that we can reliably avoid storing information that humans will not notice the absence of / changes to, while still storing everything humans do notice. It is possible that we will one day have a complete enough understanding of human perception to make some kind of general guarantees here. But that day is not today, and tomorrow doesn't look good either.

Of course. the first image of the blog post shows that you can "paint over" the largely unused area and you don't lose much of your original image. The hidden watermarks make use of this unused area so you can just paint over that area with blank data in order to "scrub" any hidden watermarks.

forgotusername6 2y ago
I'm pretty sure you could also layer the cat noise evenly over the image without significantly damaging the woman. The DCT puts all the importantly information top left, but there is nothing stopping you adding a step to distribute that information across the whole image, or using another transform that didn't have the same concentration effect
- topherclay 2y ago
  Well sure, but whatever extra step you use to encode you will also need as an extra step to decode.

tsukikage 2y ago

"Reliably" is a difficult word. If you understand how a specific watermark works, then yes, absolutely. If you want a fully general method that counters every possible thing you might come across... well. That's hard. "Imperceptible" watermarks work by altering detail humans don't notice or pay attention to. So your scrubber would need to reliably remove or change all such detail. Removing such detail is absolutely something we can do - the article mentions one way, other commenters make other suggestions, and also lossy image compression in general works by losing exactly such details from the compressed image so there's that as well. But /reliably/ get rid of /everything/, so you can be /completely certain/ no watermarks encoded in ways imperceptible to a human can possibly be left, without knowledge of the specific watermarks you want to remove or at least a way to test for their presence? You're looking at some drastic technique, in the realm of "theoretically possible but impractical"; e.g. one way might be to hand the image to a human artist, commission them to paint a copy, scan that in and use that. Note how, in the article, it's still possible to pick out the cat even as the jpeg compression level increases. If someone found a way to avoid encoding that information without degrading original image in ways noticeable to human observers, we'd all be all over that, because it would give us a way to make image files even smaller than we can now. This is an active area of research, precisely because it is key to getting better compression for sound and video to better understand how humans perceive things, what they notice and what they do not, so that we can reliably avoid storing information that humans will not notice the absence of / changes to, while still storing everything humans do notice. It is possible that we will one day have a complete enough understanding of human perception to make some kind of general guarantees here. But that day is not today, and tomorrow doesn't look good either.