Below is a list we've compiled of various Pi Day related tags at Flickr. Not everything in these tags is totally related, but most pictures here are related to Pi or Pi Day:

Piday, Pi, 314, 31415, 314159

Share your favorite equation, function, theorem, law, or property in which Pi plays a role. Try to write it out using text, or paste a link to a web page about the equation.

“Pi: A Biography of the World's Most Mysterious Number” by Alfred S. Posamentier & Ingmar Lehmann

“Pi Unleashed” by Jörg Arndt