Hi keithy397,
I'm David, and I'm happy to help you.
I understand that you want to set Irfan View as your default image application.
I've never used Irfan View, but I imagine it should be compatible with a wide range of files.
The easiest way to make compatible file extensions open by default for it. Is to configure it directly from the application.
Below is the answer related to this taken from the Frequently Asked Questions on the Irfan View website.
Q: How can I set IrfanView as my default viewer?
A: Start IrfanView, go to 'Properties->Extensions' and associate your types.
NOTE: in newer Windows versions, you must start IrfanView in ADMIN mode to change file associations. Use right mouse click on IrfanView, use the "Run as admin" menu and verify. If still not working, use the System Settings (or Control Panel): Apps => Set Standard Apps => Photo Viewer (Set default program).
Source: https://www.irfanview.com/faq.htm
I hope this helps. Feel free to ask back any questions.
________________________________________________________
Standard Disclaimer: There is a link to a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
________________________________________________________