To do that, you'd want to edit our /component/com_jfbconnect/libraries/provider.php file. Around line 241, you'll see:
return '<div class="social-login ' . $this->systemName . ' ' . $loginClass . ' pull-' . $alignment . '">
<a id="' . $loginID . '" href="javascript:void(0)" onclick="jfbc.login.provider(\'' . $this->systemName . '\');">
<img src="' . JURI::root(true) . '/media/sourcecoast/images/provider/' . $this->systemName . '/' . $image . '" alt="' . $buttonAltTitle . '" title="' . $buttonAltTitle . '"/></a>
</div>';You can add your extra code there and force the images for hover and whatnot.
You may run into some issues there because the $image value has the extension (.jpg, .png) included and that code works any time a login button is displayed. If you want a custom set of images for different sections of your site, it could be difficult (but possible) to do right. If you just want the same images everywhere with hover effects, hard-coding it there shouldn't be a problem.
I'm not sure what jQuery transition effects you want, but that's the code for rendering the buttons. I think that's a good starting point for anything you're looking to do.
Good luck,
Alex