May 5th, 2006
Shades of C.S.I.! Digital Camera Noise Ties Cameras to Photos
By Michael Santo
Contributing Writer, RealTechNews
In the past, with film cameras, it was possible to match scratches on negatives to the camera mechanism that was used to take it. Until now, it’s been impossible to find defects in a digital image that, much like a forensics expert matching a bullet or casing to a gun, would allow matching a digital camera to an image it took. This has changed, however. What use would this have? One possible example would be prosecution in child pornography cases.
It turns out that those flaws — created by such things as dust specs on the optics, interference in optical elements and natural variations between pixels — are captured on the camera’s image sensor as a unique pattern of noise.
To isolate the pattern noise created by an individual camera, Fridrich and her team used nine different cameras to take 320 images with each camera. They uploaded the images to a computer and, using software they developed, analyzed the images pixel by pixel.
By assigning values to the variations found between pixels — the pattern noise — they were able to come up with a numerical fingerprint unique to each camera. Source: Discovery News
We Say: The cool thing is that more forensics means it’s harder to get away with crimes. However, as I recently read, it also means that as jurors watch shows such as C.S.I. (and don’t you just love it when they zoom in on someone’s retina to get a reflection … and show no signs of pixelation, to boot? 
), they also become less likely to convict based on purely circumstantial evidence. Jurors frequently expect things to tie up nicely and neatly as they do on TV (the so-called “C.S.I. Effect“).
NASAdude says:
Would normalizing photos using a baseline photo taken of sintered Teflon (sometimes used as a “white” standard) avoid this problem? Even if your goal isn’t breaking the law, correcting errors color/brightness/etc on a pixel-by-pixel basis isn’t a bad idea. It’s probably a bit of overkill, though, since most cameras are good enough that it’s not worth the effort.
It would be nice if the camera could do a normalization operation itself. (I’m sure I’ll be corrected… certainly some high-end professional digital cameras are able to adjust for abnormalities in the optics and CCD by taking some reference photos of a “white” standard and a “black” (no exposure) standard, at a minimum.)
Also, how well does this digital camera “fingerprint” survive after compression? Most consumer-level cameras are using JPG or some other lossy format to save file space.
…just some random thoughts.
May 5th, 2006 at 6:29 pm
Lockergnome's Tech News Watch says:
Shades Of C.S.I.! Digital Camera Noise Ties Cameras To Photos
Michael Santo of RealTechNews writes: In the past, with film cameras, it was possible to match scratches on negatives to the camera mechanism that was used to take them. Until now, it’s been impossible to find defects in a digital image that, much lik…
May 8th, 2006 at 6:51 pm
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May 15th, 2008 at 10:45 pm