Common misconception
“Poor man’s copyright” is a myth
“The practice of mailing a copy of your own work to yourself is sometimes called a ‘poor man’s copyright.’ There is no provision in the copyright law regarding any such type of protection, and it is not a substitute for registration.”
US Copyright Office — Official FAQ
The US Copyright Office explicitly debunks the idea that mailing yourself a copy of your work provides legal protection. A postmarked envelope can be tampered with, is not searchable, and provides no statutory rights. A blockchain timestamp is significantly more robust than mailing yourself a copy — but it is still not the same as USCO registration.
What a Bitcoin blockchain timestamp does provide: a tamper-proof, publicly verifiable, independently confirmable record that a specific file existed at a specific moment in time. This is prior art evidence — not a copyright registration.