Partial Solution Through Traditional Means (Score 1)

Burn Two Copies of a write-once disc. Seal one copy in an appropriately sized tamper-proof envelope and mail it to yourself. While not a complete solution, This is equivalent to having a Notary verify that the data did exist on the postmarked date as it is on the disc. The second disk is used as part of a reference catalog to see what you have legally dated. The dated, provably unmodified data in the envelope is kept in a safe place.