1) AFAIK BitCoin doesn't have comments[1]. When people have stored data in the blockchain in the past, it was by making a series of transactions in order so lat

1) AFAIK BitCoin doesn't have comments[1]. When people have stored data in the blockchain in the past, it was by making a series of transactions in order so later those markers could be decoded to represent something else. Some services allow comments to be layered on top of transactions but that doesn't exist in the blockchain. 2) Money is sent and is rendered unspendable[2] afterwards, so I assume the idea is to send the smallest amount possible (although it seems the service takes a fee). [1] https://en.bitcoin.it/wiki/Block#Block_structure https://en.bitcoin.it/wiki/Block#Block_structure [2] http://www.proofofexistence.com/about http://www.proofofexistence.com/about