Add this to your template
<a href="http://pinterest.com/pin/create/button/?url={$smarty.server.HTTP_HOST}{$smarty.server.REQUEST_URI}&media={$link->getImageLink($product->link_rewrite, $cover.id_image, 'large')}" class="pin-it-button" count-layout="horizontal">Pin It</a>
<script type="text/javascript" src="http://assets.pinterest.com/js/pinit.js"></script>