It's easy to get the trusty old Windows Photo Viewer back -- simply open up Settings and go to System > Default apps. Under "Photo viewer" you should see your current default photo viewer (probably the new Photos app). Click this to see a list of options for a new default photo viewer. Assuming you upgraded to Windows 10 from a previous version of Windows, you should see Windows Photo Viewer as an option.
2. Double-click on your new REG file to merge it with your Windows Registry. You will need to click through the User Account Control and a few other windows to allow the file to make changes to the Registry.
I typically use taskkill, e.g. taskkill /f /im mspaint.exe or taskkill /f /im putty.exe, however my understanding is that Windows photo viewer is part of the explorer.exe process, which I don't want to terminate.
If you upgrade a PC running Windows 7 or 8.1 to Windows 10, Windows Photo Viewer will be available, and you can set it as your default photo viewer if you want. However, if you perform a clean installation of Windows 10 --- or buy a PC with Windows 10 already on it --- you can't access Photo Viewer at all. The interesting thing is that Photo Viewer is still there. It's just hidden, and you'll have to make a couple of Registry edits to have it show up. After you do that, you can then set it as your default photo viewer.
I really dislike the new "photos" app in windows 10. It's slow, takes forever to load. Is there a GPO that I can use to force machines to use windows photo viewer, or a way to disable the photos app?
I have started testing out new Horizon 7.12 cluster. I have a Windows 10 v1909 image that we are using. I have followed a best practice guide for this Master image and used the VMWare Optimization Tool with the v1909 template. The image works great in the desktops pools except for one thing. One set of users will need to drop photos on their desktop temporarily to attach to a permits program. However I think the Optimization Tool has removed the default Windows programs for it. When you drop photos on the desktop they show the icon for Windows Photos, not the thumbnail, and when you click on them they won't open. I looked at a couple of troubleshooting tips for Windows 10 that say to look for "Always show icons, never thumbnails" in the View>Options settings, but it is missing. Have any of you run across this? Should I start over with a new image for this particular pool? I have tried installing other photo viewers, but I always get the same results.