I'm not familiar with that file type. Have you tried opening it in gimp? What does file say about the file?
I suppose you could try imagemagicks convert, a2ps, or something.
Open it up in hexedit and see if there's any metadata at top. Or just use strings on the file. Are you sure it's an image file? You might try opening it with open office or mozilla.
If any of the above works, you should be able to at least do a screen capture of the image at a minimum.
$ gimp-2.2 file.djvu
$ convert file.djvu newfile.jpg
$ file file.djvu
$ strings file.djvu
$ ooffice file.djvu
You could try any of the media players on the file. But those are all just guesses. Google says...
http://en.wikipedia.org/wiki/DjVu
Perhaps one of these in wine might do the trick?
http://djvu.org/resources/
It's being promoted as the next greatest thing to PDF format. Specifically to over compress scanned images.
Or this one.
http://djvu.sourceforge.net/
Perhaps your distro has a package for it. It looks like mine does (debian/stable)
HTH
