What are you basing your statement on--are the file type extensions changing
or are you concerned about the icon which is assigned to the file?

Hi Sue,

If you want to use a specific program to view image files you can
creating a file association for the file type.
1. In Windows Explorer or My Computer, click the file you  want to open.
2. Press and hold down the SHIFT key while you use the right mouse button to
  click the file, and then click Open With on the menu that appears.
3. Click the program you want to use to open the file, and then click OK.
NOTE: If you click to select the "Always use this program to open this type
of
file" check box before you click OK, the association for the file is changed
to
the new program you select. Select this check box only if you want to change
the
default association for the file type.

Another option would be to download and install IrfanView. Select the image
types you would like to view with InfanView. Or after installed, go to
Options -
Properties - Extensions tab and select the image types there.
It's a great little image viewer and much more. And the best part, it's
FREE.
http://www.irfanview.com/