DjVu is an image compression technique that is meant to be used on scanned documents. AT&T has created a browser plugin that supports DjVu files. AT&T claims that DjVu files are 5 to 8 times smaller than GIF or JPEG images of similar quality. Some public source code is provided here, but the exciting parts of DjVu are not available.

Update: I believe this project has morphed away from AT&T and into the Open Source World. The AT&T site has been gone since 6/2002, I hope that this represents its new incarnation. I’m also moving the project status from Commercial to Non-Commercial

http://www.djvuzone.org/