[djohn]

Interesting thought, but I think that using QR codes wouldn't be worth it to card companies. They would have to store individual pictures of every card made and then create new QR codes for each and every card, not to mention printing the different QR codes on each card. It would be easier and essentially the same thing to just serial number the card and then have a database for customers to look up the card via serial number to see a picture. Even that though would be a huge undertaking for a card company to store all those pictures essentially forever (since if they only stored the images for a year or two, then after that time fakes could be made). Think about how many cards each company puts out every year and you will quickly realize the size of the database needed would be massive and the time to take pictures of every card could delay releases.
It seems like your concern is for cards where a forger takes the single color jersey out and puts in a nice multi-color patch. There are easier methods to prevent this, such as totally embedding the material (however then you wouldn't be able to physically touch it).