bootstrap button background image code example
Example: add image to boot strap button
<button class="btn btn-default">
<img src="http://i.stack.imgur.com/e2S63.png" width="20" /> Sign In with Facebook
</button>
<button class="btn btn-default">
<img src="http://i.stack.imgur.com/e2S63.png" width="20" /> Sign In with Facebook
</button>