Share Extension for public.url but only for image file?

I would like to be able to receive images from Safari in my Share Extension. To do this I need to add public.url in NSExtensionActivationRule. This works and my app can receive shared images from Safari. The problem is that my app also appears in the list when sharing a URL to a website and not an image. Now I'm looking for a way to hide my app when sharing in Safari if the URL doesn't lead to an image.