Unkown File Format

drum-uk

I have dug up some old image file from around 2005, and found they are in a file format I can't remember or find anything about on the web.

The files are bitmap images, from memory they will be most blackwhite or grayscale. They all have the extension itw and the first four characters of the file are ITW_

Does anybody know how I can read the files or convert them to something useful?