As no suitable answer was given, except for a comment by @Shoeless recommending
using AutoHotKey to survey eternally all dialog windows for this one and uncheck
the option (not recommended for such a small problem), I detail below my own
unsuccessful efforts.
The Photo Gallery is contained in the executable WLXPhotoGallery.exe.
I used Resource Hacker to view its resources, but did not find this
dialog or window as a resource.
The conclusion is that it's generated by the program at runtime,
so cannot be modified except by hacking the program's code.
I used Process Monitor to capture all registry activity of the program,
but have not identified any easily identified related setting.
So it does not look as if this option is controlled by a registry item.
The conclusion is that there is no way to uncheck that checkbox
programmatically, except by using a big canon such as AutoHotKey.
If using AutoHotKey is not an option, you will need to use another viewer.
See the article Best Free Digital Image Viewer
for better and more sophisticated image viewers/browsers
than Microsoft's Photo Gallery.
Try using Irfanview. It has a lot more options, and it remembers your last settings – hdhondt – 2015-01-27T04:23:35.187
One could get crafty using AutoHotKey to uncheck the box when the window is displayed.... but that means you'd have to be a user of AutoHotKey (https://www.autohotkey.com/)
– Shoeless – 2016-05-24T15:19:13.890Negative comment: (1) The executable WLXPhotoGallery.exe does not contain this dialog as a resource - so as it's generated by the program at runtime it cannot be modified except by hacking the program. (2) Monitoring the registry accesses of the program doesn't point to any easily identified related setting. Conclusion: Use another viewer. See Best Free Digital Image Viewer.
– harrymc – 2016-05-24T18:37:03.083What Windows OS do you have? – Steve – 2014-01-15T08:09:36.653
This is happening on Windows 7, Windows 8 and Windows 8.1. I don't know about Vista. – Larry – 2014-01-15T08:12:38.917
1
This is a problem shared by other people, and there's no resolution on the horizon.
– Steve – 2014-01-15T08:13:01.650