Actually, I was talking to someone the other day about this same problem, and spun out approximately the same solution. The important part would be a fast MD5 chip or equivalent (very fast algorithm) and the camera would only periodicallly sign the result. The question in my mind is, "do you want to sign every N frames, or only from the digital equivalent of a control track break to a control track break." (Obviously digital cameras don't have control track breaks, but a certified one would need to create an equivalent.) For use in legal matters, I'd assume you'd need to put seals on the device, or something, that were periodically inspected, to make sure the signal wasn't tampered with before hitting the signature module. I'd imagine that you _could_ incorporate the cameraperson's key, but more likely it would be some key issued by the certifying agency (a very high-rep individual or organization) that inspected the camera periodically, placed the seals, etc. A problem I see: highly realistic projections might outpace camera tech, so that you could just be projecting something and recording it. Might be thwarted by inclusion of a GPS inside the sealed part of the module. I was reading David Brin's _Earth_, and one of the things he posits are these legions of senior citizens with TruVue (or something) glasses that are apparently certified for crime reporting. -- ---------------- /\ Douglas Barnes cman@illuminati.io.com / \ Chief Wizard (512) 448-8950 (d), 447-7866 (v) / () \ Illuminati Online metaverse.io.com 7777 /______\