Am I missing something or could you just employ a download method rather than link? Maybe something like how istockphoto does it. Although the link leads to a purchase terminal, if they make the purchase it would prompt a download rather than a link they could share.

Also link shorteners + asking for credit card information immediately can get iffy in terms of trust and fraud. I understand that it is an mvp though. Later you might be able to employ a buy credits system like istockphoto does.