The programs do not store anything at all....all they do is provide a way to view certain items that you have stored in "My Documents/pictures" folder or stored elsewhere in your computer

picture viewer is designed to allow the simple viewing of jpeg, bmp, png, Tiff and gif files that ARE NOT associated with any other application such as kodak or HP picture viewer or the likes.

The fax viewer is similar as most fax files are stored as Tiff files which are clarified as raster files and read by any picture viewer that is capable of reading TIFF file associations.

They are basically the same application with just different names.