The good news is - it is still in the operating system! Using a simple hack in the registry, I was able to open image files again with Windows Photo Viewer. Run the followig .reg file, it will create 2 new keys. Repeat the steps for other file formats (png, gif, ...)
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\jpegfile\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\jpegfile\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