Je pense qu'en raison de votre première tentative d'exécution directe du fichier .dll, l'entrée "Windows Photo Viewer" pointe toujours vers le fichier .dll au lieu de rundll32, que vous ne pouvez bien sûr pas exécuter directement.
Essayez d’ajouter ce qui suit au registre:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll]
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell]
[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\Applications\photoviewer.dll\shell\print]
[HKEY_CLASSES_ROOT\Applications\photoviewer.dll\shell\print\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\print\DropTarget]
"Clsid"="{60fd46de-f830-4894-a628-6fa81bc0190d}"
( Source )
Si cela ne fonctionne pas, essayez de rechercher Windows Photo Viewer et photoviewer.dll dans le registre pour voir s'il existe des références à photoviewer.dll appelé directement (sans rundll32).