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Message:: [QUOTE="-jeffB, post: 1229837, member: 27832"]I don't know exactly what PCGS does, but I do know in general about generating compact "fingerprints" from a larger dataset (like an image). There are techniques for capturing a set of features from an image and encoding them in a short string. (It's sort of like generating a "hash code" from a computer file, but not exactly -- you can't just compare two digital photos byte-for-byte, because you'd never get exactly the same positioning and lighting.) If your technique is solid, two images of the same coin will yield the same "fingerprint", but the odds of getting the same fingerprint from two different coins (or one coin before and after tampering) are essentially zero. More importantly, the "transform" from the image to the fingerprint is one-way -- there's no feasible way to start from a fingerprint and generate an image (or a coin) that will match it. Now, there's nothing to stop PCGS (or anybody else) from doing some magic high-resolution 3-D scan of a coin and keeping the data for nefarious purposes. But the "fingerprinting" service neither requires nor implies that.[/QUOTE]