Instead of posting customer hashes to a public digital ledger, Surety creates a unique hash value of all the new seals added to the database each week and publishes this hash value in the New York Times. The hash is placed in a small ad in the Times classified section under the heading “Notices & Lost and Found” and has appeared once a week since 1995.
https://motherboard.vice.com/en_us/article/j5nzx4/what-was-the-first-blockchain
http://surety.com/digital-copyright-protection/prove-ownership
https://powerofproof.wordpress.com/