DjVu

(pronounced like "deja vu") An image compression algorithm and program developed by Yann LeCun's research group at AT&T Labs. DjVu provides high resolution digital images for distribution over the Internet. DjVu is five to 20 times more efficient than JPEG or GIF. A free web browser plug-in allows users to display DjVu images.

http://djvu.research.att.com/.