property sheet handlers on Windows 10
Try registering like below:
HKCR\.jpeg\shellex\PropertySheetHandlers\{my class id}HKCR\.jpg\shellex\PropertySheetHandlers\{my class id}
HKEY_CLASSES_ROOT seems to be deprecated:
The HKEY_CLASSES_ROOT (HKCR) key contains file name extension associations and COM class registration information such as ProgIDs, CLSIDs, and IIDs. It is primarily intended for compatibility with the registry in 16-bit Windows.
Please move your keys to HKEY_LOCAL_MACHINE\Software\Classes (or HKEY_CURRENT_USER\Software\Classes for the current user).