(left=previous image, right=next image, up=full screen, up-down=refresh, down-right=close, diagonal-up-right=zoom in, diagonal-down-left=zoom out).
HKEY_CURRENT_USER\Software\WebpImageViewer\Webp Image Viewer\Settings\WebpQuality
HKEY_CURRENT_USER\Software\WebpImageViewer\Webp Image Viewer\Settings\External[1..9]
To assign a custom title to the external application set:
HKEY_CURRENT_USER\Software\WebpImageViewer\Webp Image Viewer\Settings\ExternalTitle[1..9]