title: vertical center an image without knowing dimensions
body: <p>I have centered a lot of stuff in my webdevelopment career, but I was wondering if there is a simple way to centering an image vertically without knowing the image's dimensions. Imagine a thumbnail list I get from the database. I don't want every item to be sticking to the top of the parent div.</p>
  
  <pre><code>&lt;div id="wrapper"&gt;
      &lt;div id="parent"&gt;
          &lt;img src="path/i/got/from/database/image.png" /&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>