How to align an image dead center with bootstrap

I’m using the bootstrap framework and trying to get an image centered horizontally without success..

I’ve tried various techniques such as splitting the the 12 grid system in 3 equal blocks e.g

<div class="container">
    <div class="row">
      <div class="span4"></div>
      <div class="span4"><img src="https://stackoverflow.com/questions/10879955/logo.png" /></div>
      <div class="span4"></div>
    </div>
</div>

What’s the easiest method to get an image centered relative to the page?