The login buttons are the only ones that you can provide an image currently. We use each social network's javascript libraries to render the social sharing buttons.
Generally, each social network provide options to size/style the buttons buttons. You'd be able to pick the right size, possibly width etc. Depending on how you're displaying the buttons using JFBConnect, you'll find these parameters in either the SCSocialWidget module, EasyTag or Content Plugin.
-Melissa
I want to choose the type of social share buttons I want.
