When you use the {JFBCLogin .. tag, you can use a comma separated list of different providers to show. The image parameter will apply to all providers listed. So the tag:
{JFBCLogin providers=facebook,twitter,google image=large.png}
Will show all 3 social login buttons using the /google/large.png, /facebook/large.png and /twitter/large.png files.
I hope that helps, but if you need more help or details, just let us know.
Thanks,
Alex