Thanks for the reply. This seems really illogical how this is presented currently. I say that because the entries in the advanced area are not for all extension types that the software currently works with. They seem to be just specific exceptions.
What I mean is that txt, php etc are not listed there. Tortoise correctly just understands it should use the
external tool that I've specified in the main "Diff Viewer" settings screen.
However when it comes to images, these are also NOT listed in this advanced screen. So as there is no special exception setup for them as default, why is the program handling them differently and not just blindly calling the external program I've specified like it does with a text file ?