Change header from text to image on tumblr?

I have been having trouble with the code on tumblr.

The image i want to make as my header has a size of 500px by 268px. I was following the instructions on this particular question: http://www.fluther.com/82664/change-header-from-text-to-image-on-tumblr/

From that I changed this
<a href=”/” class=“blogtitle”></a>
to this
<a href=”/” class=“blogtitle”><img src=“http://imgur.com/Y0FTh.png”></a>

Yet I cannot see the picture. I am a bit confused.

Thank you for your help