I've started working on this site but I had a concern. Yesterday, I received some brand new bills from a convenience store and noticed the sequentiality (sequence-ness? sequence-nicity?) of the serial numbers.

If all you needed was the right serial number to unlock an account, how easy would it be to create a bot to do it? Would a captcha help?

I know you could write a code on the bill along with the url, but I was kinda excited about using even an unmarked bill as an advertisement for bitcoin.