Beats me.
I did find a reference to some instances of 'interference' between IE6 and Norton/McAfee anti-virus products. One of the symptoms was non loading of images, and the fix was to decrease the security settings, or uninstall and reload the AV.
Apparently if you right click on the page and chose 'show image' it does then appear.
Only other suggestion (straw-grasping) is to verify the file-to-program associations are still OK in Windows Explorer (although I would have expected a pop-up if it couldn't find the program).