How could I find out the path to the current desktop image, for Windows 8

The two registry keys below both store the original path of the current wallpaper image:

HKEY_CURRENT_USER\Control Panel\Desktop\TranscodedImageCache
HKEY_CURRENT_USER\Control Panel\Desktop\TranscodedImageCache_000

They're in Unicode format, upon decoding that, one will have the full path to the current wallpaper image.

1. Go to Windows Run Command (WinLogo+R)
2. Type in: %AppData%
3. In the 'Roaming' folder, go to 'Microsoft', then 'Windwows', then 'Themes', and lastly 'CachedFiles'
4. Copy the wallpaper file.

Check the HKEY_CURRENT_USER\Control Panel\Desktop\Wallpaper REG_SZ (string) value. This will show you the path to the TranscodedWallpaper.jpg currently in use.