For Windows 10 [verified]: Windows Photo Viewer Download

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.jfif\UserChoice] "Progid"="Applications\photoviewer.dll"

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.gif\UserChoice] "Progid"="Applications\photoviewer.dll" windows photo viewer download for windows 10

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.tif\UserChoice] "Progid"="Applications\photoviewer.dll" windows photo viewer download for windows 10

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.jpe\UserChoice] "Progid"="Applications\photoviewer.dll" windows photo viewer download for windows 10

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts.dib\UserChoice] "Progid"="Applications\photoviewer.dll"

Microsoft replaced it with the (a UWP app) starting with Windows 8 and 10. However, the old Windows Photo Viewer (from Windows 7 and 8) still exists in the system files of Windows 10 — it's just not set as the default image viewer.