IW44 is file format is designed to store bitmaps of scanned images, especially those containing text and line drawings. The format is increasingly important because of its use in the Million Book Project and the One Laptop per Child project. It can also be .IW4 when a 3 digit extension is needed.
This is a subset variant of DJVU that uses DjVu IW44 wavelets, hence the name. It can be used for color or grayscale images. This is the preferred mode for creating a DjVu image which does not require separate layers for encoding the text and the background images.
Generally any reader capable of reading DjVu can also read IW44 but the reverse is not necessarily true as IW44 is simplified from DjVu.