If an image from a marccd (tif format) is called .img - which it apparent is sometimes - ImageViewer tells it is loading but no image comes up nor does an error message. If the image is renamed to .tif or .mccd it is read normally. Fabio openimage uses a magic number hence it uses tifimage even if the extension gives a hint to another format. I have a test image - it was too big to attach.
If I rename or copy a tif image to have an img extension I can open the file with ImageViewer in RC7 on Linux.
Can you make your marccd test file available somehow ?