A digital or physical copy of a receipt. But then how would they know the receipt is theirs? Well, they don't. There are a subset of users who have bit for but copies. I think if they came into some legal trouble having that vs a rip would be better since the data is in tact the same way it was when purchased. Can I easily be called a backup.
I'm not your lawyer and I'm definitely not a lawyer anyway. Just playing Devis Advocate.