If you are like me, and disabled UAC then Windows 10 Photo App won't launch. Nor will any "app" (Metro stuff), but personally I hate all that garbage, its for tablets not PC's. Anyway long story short, this is how you restore the old windows photo viewer App.
Note: This is only necessary on "fresh" Windows 10 Installs. (I will never "upgrade" an OS, always fresh!)
Merge Activate-Windows-Photo-Viewer-on-Windows-10.zip reg file and then Photo View should show up when you right click open with >> choose default program.
Taken from HowToGeek.