At 11:52 PM 8/24/04 -0400, Dave Emery wrote:
Just a random distraction from the normal topics (but not completely irrelevant either)...
Highly relevant sir.
He told me that especially in the low end camera market NO sensors used were completely free of anomalous pixels (black, white, dim, bright etc) and much of the actual processing in digital camera firmware was related to masking or hiding the inevitable defects which apparently can include (at least in CMOS sensors) entire rows or
columns >that are bad.
Kinda like disk drives and DRAM arrays. Its all about yield. Covering up mistakes transparently.
This got me thinking - clearly these concealment patches are not completely undetectable in families of (multiple to many) images taken with the same exact camera... and for the most part the defects are born with the sensor and change little over time if at all. And with few exceptions they are random, and different for each sensor.
Perhaps, but the jpeg-ization might lose these, or at least the image "unicity distance" might require many more pictures than a careful steganographer will publish.
Cypherpunk relevance (marginal perhaps), but the ability to say that a particular image or set of images came from a particular camera COULD have legal consequences for those bent on activities someone thinks of as unfriendly to their interests...
Very relevant, traffic analysis and fingerprinting (intentional or not) are always tasty subjects. One question for the court would be, how many *other* cameras have column 67 disabled? One of every thousand? And how many thousand cameras were sold? Pope Major Variola (ret)