Prove a file existed, unchanged, by a certain date, or check a proof someone sent you. Free, using OpenTimestamps and Bitcoin, with no coins or wallets involved. The file is fingerprinted in your browser and never uploaded. We've timestamped 978 of our own documents this way, with no failures.
https://makeprivacy.org/tools/timestamp/
#OpenTimestamps #Bitcoin #DigitalEvidence #OpenSource