You have to pass in the html option to when you initialize .tooltip. e.g.
<div class="cart">
<a data-toggle="tooltip" title="<img src='http://getbootstrap.com/apple-touch-icon.png' />">
<i class="icon-shopping-cart"></i>
</a>
$('a[data-toggle="tooltip"]').tooltip({
animated: 'fade',
placement: 'bottom',
html: true
});
See the example fiddle