If I were the NSA, I'd have a modified graphics driver which overlays pseudorandom very faint grey dots over the screen at all times. A 254 254 254 pixel hidden amongst all while pixels isn't visible, yet thousands of them across a page will encode significant amounts of information, even in the face of quite severe image compression and low quality.
The dots could be based on the computer, currently logged in user, and timestamp.
Then later, if any screenshot or screen photo is leaked, you can decode the dots to identify the source.
You think that they would even be picked up when you take a picture with a camera? Between the external camera, and then compression, I don't think that the 254 254 254 pixels are going to make it into the final image. They might not even make it into the initial picture - screen backlighting consistency, etc, is going to wreak havoc on that from the start, before we even get into sensor noise, etc on the camera, any smudges on the lens, all before it even gets saved a jpg
There's an amazing way of encoding data called "gold codes". By having enough pixels like this, you can correlate the image with the expected pattern, and successfully extract data even though no individual pixel is visible.
It's used in GPS transmissions to allow decoding signals considerably weaker than the background noise. Because the receiver is aware what the signal should look like, it can extract it despite all the noise by averaging across all the samples.
It does require perfect alignment though, which might be tricky considering camera lens warping, etc.
If I were the NSA, I'd have a modified graphics driver which overlays pseudorandom very faint grey dots over the screen at all times. A 254 254 254 pixel hidden amongst all while pixels isn't visible, yet thousands of them across a page will encode significant amounts of information, even in the face of quite severe image compression and low quality.
The dots could be based on the computer, currently logged in user, and timestamp.
Then later, if any screenshot or screen photo is leaked, you can decode the dots to identify the source.
You think that they would even be picked up when you take a picture with a camera? Between the external camera, and then compression, I don't think that the 254 254 254 pixels are going to make it into the final image. They might not even make it into the initial picture - screen backlighting consistency, etc, is going to wreak havoc on that from the start, before we even get into sensor noise, etc on the camera, any smudges on the lens, all before it even gets saved a jpg
There's an amazing way of encoding data called "gold codes". By having enough pixels like this, you can correlate the image with the expected pattern, and successfully extract data even though no individual pixel is visible.
It's used in GPS transmissions to allow decoding signals considerably weaker than the background noise. Because the receiver is aware what the signal should look like, it can extract it despite all the noise by averaging across all the samples.
It does require perfect alignment though, which might be tricky considering camera lens warping, etc.