That device would be very useful for crooks.

[EDIT] Combined with some custom software, that device could be the easiest way to copy someone's CC information. A waiter could swipe the card on his iPhone, before running it on the restaurant's POS machine.

Waiter's already have plenty of time to get your credit card information. It does not take any longer to take a picture of the front and back of your card. Waiter's (and other POS workers) have been stealing credit information in low tech ways since credit cards have existed.

If someone's got your credit card--Square isn't going to make it any easier to make unauthorized purchases. It's probably more work given how easy it is to use someone else's card in retail and restaurant POS.

Unlike a digital camera, or, say a pen and paper to write down the cc number?

and prostitutes.

and drug dealers.

Drug dealers do love proof of purchases.

How else would you prove your eligibility for the bulk discount?