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The miner has to manually enter the solution to that captcha, and send the solution over to the other 8 nodes. The verification of the CAPTCHA from the other 8 nodes is automatic since they have the database of CAPTCHAS on their computer just need to cross validate between each other.
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How do you keep the miners from having a database of CAPTCHAS on their computer? If they have the database, can't they just write a program to look up the entry in the database and return the correct answer?
Hmm interesting point, indeed if the random number is generated on the PC the miner knows and he can lookup the captcha solution for it in the database.
Any solutions how to fix this?
Maybe perhaps the captcha database should not exist, and the CAPTCHA should be generated on the go by the client, and then the CAPTCHA should be sent around, with the miner's answer, to all miners to validate and whatever answer reaches say 90% threshold accuracy, that will be the correct one, and every miner who answered the wrong question won't get a bonus.