I know that this question has already been asked, but the HTML I am looking at has been written in a strange format, in my opinion. I already looked at this thread: How do I mak
Assuming in the tumblr Customize menu, you have a header image uploaded to header and the option IfHeaderImage checked in the Tumblr Customize menu:
{block:IfHeaderImage}{/block:IfHeaderImage}
The link tags wrap around the img tag, rendering that image a link. Change the INSERTURLHERE to the URL of the site you wish to link to.
Otherwise, if you decide not to have a header image, gersande's method works.