<script>function fb_like() {
url=location.href;
title=document.title;
window.open('http://www.facebook.com/sharer.php?u='+encodeURIComponent(url)+'&t='+encodeURIComponent(title),'sharer','toolbar=0,status=0,width=626,height=436');
return false;}</script>

<a href="http://www.facebook.com/share.php?u=URL-TO-SHARE" onclick="return fb_like()" target="_blank">Custom Image Here</a>

http://dsnacks.me/web/custom-facebook-like-button-design

Just add an image... try it.

Easy Facebook Like button from designer snacks

simple, button, facebook

JavaScript