In windows 10, Windows Live Photo Gallery displays icons and not thumbnails. I have tried EVERYTHING with no results. (Well, not quite everything. dod not do the command prompt thing.) I finally resorted to uninstalling it, but now I cannot find any download to reinstall it.
Start button > Control Panel > classic view > Folder Options > View tab >UN-check the first box " Always show icons never thumbnails " > OK
Microsoft website prompts Windows Photo Gallery was a part of Windows Essentials 2012 suite reached end of support on January 10, 2017. It is no longer available for download. But I find that you could try to download it from the link below.