Someone I used to work with did this. He swiped credit cards through a small reader that stored the numbers which he then took to some guy who made fake cards from the credit card information in which the person I worked with stole.
Eventually he got caught and the secret service investigated him. He managed to get off easy though because he snitched on the guy who made the cards.
One of the foreman at work got scammed like this. Best we can figure it happened when he was in Texas for some training some restaurant employee etc, must've scanned his card and sold the scans for someone to create a fake. It was a couple months later looking over the visa bill that we noticed $4000 in the Phoenix / Scotsdale area had been spent at various wal-marts and such buying mostly gift cards and pre-paid cellphone minutes.
I looked into it and discovered that the chance of randomly hitting a valid card is almost nil. The card number itself follows luhn but also the expiration date AND an equivalent of the cvv is encoded in the stripe but it is *NOT* the same as the number printed on the back of the card. The format of the magstripe varies from one card to another but there is a basic format followed that can be used to recreate cards. My final idea was to look at the next extrapolated number in the luhn series, use the same expiry, and then guess at the internal CVV. Its only 3 digits, so if you made 1000 fakes, one would really solve the internal algorithm - which i believe would be enough to authorize say automated gas pumps but may still be invalid or unissued.
I researched this using scans from all our company credit cards plus some of my own, and really had no intention of using them to scam but only to see how hard it would be to generate a random card that would satisfy the math, but when the secret service busted my friend for passing the novelty ids and novelty checks I had printed him... they confiscated my reader/writer and charged me with possession of the cards (which was nothing more than a cmasterIV list with my companies cards highlighted so i could find a gap card to play with)