As the topic, I would need something that can open .mdi files. I tried Microsoft Office Picture Manager and Picture and Fax viewer but no luck. Only .tif files can be opened.
The official page about Microsoft Document Imaging Format (MDI) states that MDI files can only be opened or edited in Office Document Imaging. If you have this utility but can't open .mdi files with it, try the resolutions given in the following Microsoft article:
KB 926198: "An .mdi file does not open in the Microsoft Office Document Imaging program that is included in the 2007 Office programs"
Alternatively, a quick Google search brings a 3rd party program which is a free tool that can view .mdi files: MDI Viewer 1.0.32