Sangaku - Japanese Mathematical Tablets
The things you see along the top of the webpage are called sangaku, or Japanese mathematical tablets. They were made by untrained farmers hundreds of years ago, yet often coincided with and occasionally preceded similar results by European mathematicians.
There was been a small uprising in interest since a Scientific American article by Dr. Tony Rothman in 1998. Rothman has since followed up by releasing the third book on this list with Fukagawa Hidetoshi.
A History of Japanese Mathematics
Smith, David E. and Yoshio Mikami. Open Court Publishing Company, New York, ©1914. (It has come to my attention that this book was just reprinted in April of 2004.) - ISBN 0486434826
The Development of Mathematics in China and Japan
Mikami, Yoshio. Chelsea Publishing Company, New York, 1974. - ISBN 0828401497
Sacred Mathematics: Japanese Temple Geometry
Fukagawa Hidetoshi and Tony Rothman. Princeton University Press, ©2008. - ISBN 9780691127453