There is a service that uses bitcoin blockchain to prove that certain data exists at a certain moment of time [link removed] . This is done by generating a bitcoin transaction (unspendable) to two specially crafted addresses.
This is a very inefficient and destructive way to perform this tasks. I would not recommend using or promoting this service.
I wrote a system that does the same thing, but without spamming the blockchain with unspendable junk.
I never released it. If there is some demand for such a service, I can finish it up and put it online.
Wouldn't the easiest be to use the hash of the file as the private key like a brain wallet and send to the address and empty the address back to another address you control? It's very simple and easily checked by anyone and doesn't leave coins unspendable.
You could even create a text file listing many hashes of files on the computer and prove them all in one transaction just by creating an address from the hash of the text file and bounce the coins to the address and back.