It is well documented that one should consider that all modern printers perform steganography / watermarking in the back of their users


Is such a feature also documented / are there rumors of similar features with the raw pixel matrix coming out of modern digital cameras? (I am not talking about exif of other metadata, only raw pixel data).

Edit: I am not talking about naive steganography as done by adding dots, but also advanced methods, see comments.

  • No. Steganography and digital watermark can be much more subtle than adding dots. For example DRM of music, frequency space steganography, methods based in spread spectrum. – Zorglub29 Nov 11 '17 at 13:54
  • I am pretty sure that you are wrong, because digital images do have some level of 'real' noise and randomness (coming from quantic effects on the chip, ADC thermal noise, and other such real works processer). This means possibility to hide information. A simple google search will give you a lot. – Zorglub29 Nov 11 '17 at 14:06

Yes - well, sort of, albeit (as far as I know) unwittingly. I attended a conference where one of the relators was prof. Jessica Fridrich reporting on the identification of digital image sources. You can probably start your search on her page, here.

To be clear, this is nothing like intentional yellow-dotting performed by some printers, and cannot be used to trace a picture to a camera unless you also possess that camera and can take other pictures to compare.

What happens is that every CCD chip has subtle variations that can be recovered through frequency analysis from the original picture data, and these variations are manufacturer and chip specific. This allows, with a certain error margin, to:

  • given two pictures, determine whether certain areas of one picture are original or whether they come from a different source (the patterning in those areas is not consistent with the CCD)

  • given two pictures, or a picture and a camera, determine whether the picture came from that camera or not.

It would be extremely easy to make this system more reliable, by e.g. laser etching the CCD chips with a unique pattern. This would not be visible to the naked eye when inspecting the pictures, but the information could be recovered.

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    You are correct. It is, at least theoretically, possible to work out what camera was used to take an image. This is based on statistical analysis of the noise that the sensor introduces to the image. AFAIK, you would have to have access to the camera though so there is no known absolute tracking by camera manufacturers, unlike printers. – Julian Knight Nov 12 '17 at 1:21

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