Here is registry script to enable Windows Photo Viewer on Windows 10
Windows Registry Editor Version 5.00
; Created by: Shawn Brink
; Created on: August 8th 2015
; Updated on: November 15th 2017
; Tutorial: https://www.tenforums.com/tutorials/14312-restore-windows-photo-viewer-windows-10-a.html
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open]
"MuiVerb"="@photoviewer.dll,-3043"
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Bitmap]
"ImageOptionFlags"=dword:00000001
"FriendlyTypeName"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\
00,46,00,69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,\
77,00,73,00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,\
00,65,00,72,00,5c,00,50,00,68,00,6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,\
65,00,72,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,35,00,36,00,00,\
00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Bitmap\DefaultIcon]
@="%SystemRoot%\\System32\\imageres.dll,-70"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Bitmap\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Bitmap\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.JFIF]
"EditFlags"=dword:00010000
"ImageOptionFlags"=dword:00000001
"FriendlyTypeName"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\
00,46,00,69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,\
77,00,73,00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,\
00,65,00,72,00,5c,00,50,00,68,00,6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,\
65,00,72,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,35,00,35,00,00,\
00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.JFIF\DefaultIcon]
@="%SystemRoot%\\System32\\imageres.dll,-72"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.JFIF\shell\open]
"MuiVerb"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,\
69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,\
00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,\
72,00,5c,00,70,00,68,00,6f,00,74,00,6f,00,76,00,69,00,65,00,77,00,65,00,72,\
00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,34,00,33,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.JFIF\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.JFIF\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Jpeg]
"EditFlags"=dword:00010000
"ImageOptionFlags"=dword:00000001
"FriendlyTypeName"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\
00,46,00,69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,\
77,00,73,00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,\
00,65,00,72,00,5c,00,50,00,68,00,6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,\
65,00,72,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,35,00,35,00,00,\
00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Jpeg\DefaultIcon]
@="%SystemRoot%\\System32\\imageres.dll,-72"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Jpeg\shell\open]
"MuiVerb"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,\
69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,\
00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,\
72,00,5c,00,70,00,68,00,6f,00,74,00,6f,00,76,00,69,00,65,00,77,00,65,00,72,\
00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,34,00,33,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Jpeg\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Jpeg\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Gif]
"ImageOptionFlags"=dword:00000001
"FriendlyTypeName"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\
00,46,00,69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,\
77,00,73,00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,\
00,65,00,72,00,5c,00,50,00,68,00,6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,\
65,00,72,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,35,00,37,00,00,\
00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Gif\DefaultIcon]
@="%SystemRoot%\\System32\\imageres.dll,-83"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Gif\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Gif\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Png]
"ImageOptionFlags"=dword:00000001
"FriendlyTypeName"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,\
00,46,00,69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,\
77,00,73,00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,\
00,65,00,72,00,5c,00,50,00,68,00,6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,\
65,00,72,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,35,00,37,00,00,\
00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Png\DefaultIcon]
@="%SystemRoot%\\System32\\imageres.dll,-71"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Png\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Png\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Wdp]
"EditFlags"=dword:00010000
"ImageOptionFlags"=dword:00000001
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Wdp\DefaultIcon]
@="%SystemRoot%\\System32\\wmphoto.dll,-400"
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Wdp\shell\open]
"MuiVerb"=hex(2):40,00,25,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,\
69,00,6c,00,65,00,73,00,25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,\
00,20,00,50,00,68,00,6f,00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,\
72,00,5c,00,70,00,68,00,6f,00,74,00,6f,00,76,00,69,00,65,00,77,00,65,00,72,\
00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,33,00,30,00,34,00,33,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Wdp\shell\open\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\PhotoViewer.FileAssoc.Wdp\shell\open\DropTarget]
"Clsid"="{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Image Preview\command]
@=hex(2):25,00,53,00,79,00,73,00,74,00,65,00,6d,00,52,00,6f,00,6f,00,74,00,25,\
00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,72,00,75,00,\
6e,00,64,00,6c,00,6c,00,33,00,32,00,2e,00,65,00,78,00,65,00,20,00,22,00,25,\
00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,46,00,69,00,6c,00,65,00,73,00,\
25,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,73,00,20,00,50,00,68,00,6f,\
00,74,00,6f,00,20,00,56,00,69,00,65,00,77,00,65,00,72,00,5c,00,50,00,68,00,\
6f,00,74,00,6f,00,56,00,69,00,65,00,77,00,65,00,72,00,2e,00,64,00,6c,00,6c,\
00,22,00,2c,00,20,00,49,00,6d,00,61,00,67,00,65,00,56,00,69,00,65,00,77,00,\
5f,00,46,00,75,00,6c,00,6c,00,73,00,63,00,72,00,65,00,65,00,6e,00,20,00,25,\
00,31,00,00,00
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Image Preview\DropTarget]
"{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A}"=""
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Photo Viewer\Capabilities]
"ApplicationDescription"="@%ProgramFiles%\\Windows Photo Viewer\\photoviewer.dll,-3069"
"ApplicationName"="@%ProgramFiles%\\Windows Photo Viewer\\photoviewer.dll,-3009"
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Photo Viewer\Capabilities\FileAssociations]
".jpg"="PhotoViewer.FileAssoc.Jpeg"
".wdp"="PhotoViewer.FileAssoc.Wdp"
".jfif"="PhotoViewer.FileAssoc.JFIF"
".dib"="PhotoViewer.FileAssoc.Bitmap"
".png"="PhotoViewer.FileAssoc.Png"
".jxr"="PhotoViewer.FileAssoc.Wdp"
".bmp"="PhotoViewer.FileAssoc.Bitmap"
".jpe"="PhotoViewer.FileAssoc.Jpeg"
".jpeg"="PhotoViewer.FileAssoc.Jpeg"
".gif"="PhotoViewer.FileAssoc.Gif"
".tif"="PhotoViewer.FileAssoc.Tiff"
".tiff"="PhotoViewer.FileAssoc.Tiff"
Copy paste into notepad, save it to file with .reg extension and merge it.
References: