Various bits of PHP / HTML to customize this theme.

1. Manually add a header image block

These steps are all documented in the video at the end of this block, skip to it for more help.

First add a new text box using the Thesis Skin Editor in the Header -> Title Area block, under "Site Title". In the block options change the HTML Tag drop down to No HTML wrapper.

After you add the text box, save your template and go to Thesis -> Skin Content and in that boxes options paste something like the below (change the URLs / image source URL):

<div id="title_area">
<a href="http://mysiteurl.com"><img width="135" height="75" title="click to return home" alt="click to return home" src="http://mysiteurl.com/wp-content/uploads/2013/09/logo.jpg" id="thesis_header_image"></a>
<h1 id="site_title"><a href="http://mysiteurl.com">My Site Name</a></h1>
</div>

Now add your new custom box to your other templates in the skin editor to have it show up on all your pages / posts.

Video Walk Through of Above