File associations

I made a change in DO8 to show pdf thumbnails as mini pdfs. But now all images, when double clicked, open in DO8. How do I get the file association for images to point to IrfanView in DO8? (Images open in IrfanView using Explorer.)

Does this do the trick?

[How to stop the Opus image viewer from being used by default)

Nudel, you're a genius. Thanks heaps