Just a random distraction from the normal topics (but not completely irrelevant either)... I happened to spend a few minutes yesterday talking with an individual who participated in the development of both low and high end digital cameras for the commercial mass market. 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. 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. Thus it ought to be possible to detect with reasonable probability that a particular image or (much easier) that a particular family of images was likely to have originated with a particular camera. A kind of digital fingerprint if you will... 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... Of course the headers of jpegs from cameras (and maybe elsewhere) often contain serial numbers and other identifying information so to the first order this is irrelevant to average users, but interesting none the less. -- Dave Emery N1PRE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493