What is Proof.ink? Proof.ink's service is pretty straightforward. If you have a document of which you want to know with 100% certainty that it's contents has not been changed, tampered with or altered in any form, use Proof.ink. Proof.ink works by fingerprinting your file (no matter how big), without the need to upload it, inside your browser. The result of this calculation is a unique SHA256 hash / fingerprint of your file. By enabling you to store the fingerprint publicly on the Steem blockchain, Proof.ink can guarantee the integrity of the fingerprint of the file as how it was created at a given time by a given user. This way others can use this service to validate the fingerprint on the blockchain and against the file they receive. The Steem chain serves as a public accessible ledger with provable immutability at it's core, for a trustless public store of the derived file's fingerprint.