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Assume I publicly release and announce a program to decode the child porn from the block chain, such that everyone knows and can easily confirm that there's child porn in the block chain.
Publicly announce where?
Publicly announce it here and one of the moderators will delete it faster than you can type 'rm'.
Announce it on your own website and I'd encourage the legal authorities and/or your ISP to shut you down.
Announce it in IRC chat or via a Freenet/TOR/i2p hidden service and I would personally encourage everybody to shun and /ignore you... and very few people will hear your announcement, anyway.
I suppose you could try to get a journalist or government interested in causing trouble for bitcoin to publicly announce it. If you did, I would ask as loudly as I could why the journalist or government is complaining about innocent bitcoin users instead of trying to track you down and prosecute you.