Thanks, and glad you like the extension!
Unfortunately, if I understand you request correctly, what you're looking for isn't possible. Facebook does not want you to overwrite their image as they want their brand to always be the same across sites. The only flexibility they give is the size of the button and the text you can put in there ("Login with Facebook").
I'm providing a link below to a page which gives examples of how to use a custom image. We won't implement that in JFBConnect because the last time we checked (and this may have changed), the Facebook policy states you shouldn't override their image.
sarfraznawaz.wordpress.com/2010/12/11/cu...ebook-connect-image/
Hope this helps, and let us know if you have any other questions!
Facebook Login button style
