DjVu is an interesting file format:
- Better than JPEG for photos. (see c44)
- Can compress with limited amount of colors (see cpaldjvu)
- Incredible compression ratio for black&white (see cjb2)
- Support multipage (like TIFF or PDF).
- The ammount of memory required is minimal (fast zoom-in and zoom-out). Huge pictures are easily managed (thanks to wavelet compression).
- It supports OCR.
All this make it very suitable for many purposes (I use for both storing pictures and documentation). It is one of the supported formats in http://www.openlibrary.org
More information here: