Protocol
Your device hashes the file and only the hash is sent; we keep the hash and the proof file, never the file.
The receipt is pending until a real Bitcoin block includes the hash; then it reads In block N, which means these exact bytes existed by that block, not that the words are true.
Anyone can check the proof file against the original, without an account and without us.
We keep the hash. You keep the file. Bitcoin keeps the time.
Timechain means the Bitcoin chain used as the clock. We do not run a second chain.