Add to your header above the body tag
<script type="text/javascript" src="http://assets.pinterest.com/js/pinit.js"></script>

Edit and add to your page where you want your button to appear.
<div class="socialIcon-box"><a href="http://pinterest.com/pin/create/button/?url=http%3A%2F%2Fyourdomain.com&media=<?php bloginfo(template_directory); ?>/images/youricon.png&description=Site%20Name%20and%20Description" class="pin-it-button" count-layout="horizontal"><img src="<?php bloginfo(template_directory); ?>/images/youricon.png" /></a></div>

http://flashalexander.com/pinterest-social-button-link/

Edit and add code as indicated to use a custom Pinterest button and link on your WordPress site. Can be adapted for any site of course. No need to signup a pinterest account to add Pinterest action for clients.

Add Custom Pinterest Button to WordPress or Any Site

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