Btw, the .wtv files in my example were created by Windows Media Center, which is also the default program of .wtv, not VLC. I do not create any video files using VLC.
Lady Fitzgerald
The orange and white cone in the lower right of the thumbnails for .wtv is the VLC logo or icon.
I believe if you check the Properties of these files you will find that their open with is associated with VLC.
If you click or double click on one of these .wtv files VLC should be the program that opens it.
Give it a try and post if I'm incorrect. I would like to know.
With a right click on an .iso file & selecting "Change" .
In the window that pops up select "other programs" by the + sign.
VLC should be there . Select it. If it isn't there use "Browse" to find VideoLan/VLC in Program Files.
Usually the vlc.exe is the correct association.
See if the .iso files now have thumbnails like the .wtv files.
I will give this a test on my OS and see .
Usually I keep media files associated with Windows system file that does nothing.
That way they don't auto open a specific software. The icon looks like a blank page.
No problem to check and then change it back.
I did some testing .
When I associated an .iso file with VLC all I got was the orange & white VLC cone.
I also tested with a .wmv file .
When set to View/medium icon or larger the .wmv's have a thumbnail .
If I associate them with VLC . The orange & white cone is added to the thumbnail as in your photo.
The result of my tests are no thumbnail for an .iso like you wanted.