The code didn't come through (our filters sometimes strip the code). You can use the code below anywhere, in an article, module, etc to use the custom image tag. However, depending on your Joomla settings, HTML/Javascript code can be stripped when try to save the article.
<a href="javascript:void(0)" onclick="jfbc.login.login_custom();"><img src="http://yoursite.com/link-to-image.jpg" /></a>
One other thing you can do is use the Content - Load Modules plugin that comes with Joomla. Simply create an SCLogin module with the options you want (including the custom image link), set it to a position of "custom_sclogin". Then, in your Joomla article, use {loadmodule custom_sclogin}. That will load the entire SCLogin module and give you even more flexibility over the options.
Hope that helps, but if not, just let us know!
Thanks,
Alex