In IGN's review of the PlayStation 3 card-based title The Eye of Judgement, they note that the camera-based card detection can actually be fooled, which may enable a type of cheating.
The game has a cheat-proof registering function, which forces players to pre-register their decks by scanning each card before games to prevent "under the table" card switching action. This is a good measure, but they didn't factor in that someone might try to copy "good" cards.
It seems that high quality color copies of cards can be detected as real ones, which would let cheaters simply print off cards they don't have to play with. IGN notes that this does not affect gameplay, as cheaters will still have to follow in-game rules while in a match, but they'll still be playing with cards they don't own.
Of course, only a total douche would copy cards to win, but as we all know, there are plenty of cheaters out there that would go to these lengths to win.