[flogic]

OCR would be grungy whereas the magnetic stripe is the intended direct machine interface. When you attempt to connect a machine to a human interface all sorts of annoying things can happen. Even if it's simple in theory, the amount of errors generally jumps.

[grandalf]

True enough, but we're talking about reading around 20 characters that are raised from the plastic and typically printed using the same font on all cards. As far as OCR tasks go, it's pretty simple, and OCR is an established, evolved technology.