I'm glad to hear that helped show the buttons. You can drop any named files you want into that directory and JFBConnect will show them as options. The only thing to be aware of is that the JFBCLogin easy-tag has only one image parameter:
{JFBCLogin image=blah.svg}
With that tag, all the social login buttons enabled will be shown with the 'blah.svg' image from their own provider directory.
We don't really see much of an SEF benefit from having your image names align with a social network, but if you can elaborate on why you think that's beneficial, we're curious.
Thanks,
Alex