PokerTH is a really enjoyable open-source online poker game.
These are transparent cards to give a layered glass sheet effect. Works pretty well on the default table style, although darker backgrounds in the custom styles can make it difficult to see the black cards. So far no evidence that it gives you better cards
The zip file includes Gimp format files for anybody who feels the urge to improve upon this.
Please go to the PokerTH website for installation instructions. Support? From me?? Don't even think about it.