I'm very fascinated by Transformation Decks, which are unique decks of playing cards where the pips have been incorporated into a larger artistic image. I've been doing some research into these beautiful playing cards, and have written a series of three articles that covers the history of transformation decks, showcasing many pictures of some of the best examples.
Here are links to the three articles, which you'll find elsewhere on the site:
Transformation Decks (Part 1) - 19th Century
Transformation Decks (Part 2) - Late 20th Century
Transformation Decks (Part 3) - Modern Era