[mrduncan]

The numbers on cards become a lot harder to read after the coloring wears off of the numbers. Even as a human it can be hard to read them at times depending on the lighting.

Card layouts also vary a lot, even from the same issuers (for example: the Amex PASS).

Reading the mag stripe prevents fraud and therefore is subject to lower fees by CC companies.

Not to mention, having someone take a picture of my credit card would spook me out a little (yes, even if I'm familiar with the product).

[grandalf]

To your last point, how is letting someone scan the magnetic stripe less spooky?

Considering that augmented reality app that translates words on signs in real time, I suspect there is far less entropy in the raised numbers on a credit card... though you may be right that the variety of layouts would make it harder than it would at first seem.

[mrduncan]

Technically, it is not at all.

Socially however, I'd wager that fewer people would let you take a picture of their card compared to swiping it. People are simply used to having credit cards swiped, they aren't used to having pictures taken of them.