We've updated the card images that display when you redeem booster packs and look at your nation status screen. The design of the card now shows which cards are rare - rare cards have a gold border design instead of a white bar (compare the borders on the cards above - the Black Dragon and Flaming Catapult are rare).
We hope this makes it easier to keep track of your cards. And for those of you looking to update your guides/website, we'll release an archive file soon that contains all of the card images.