Custom Header Thesis 2 - add this to the custom.php in the skins folder. Make sure you don't have a image uploaded in "Thesis -> Header Image"

Custom Header Thesis 2

global $thesis;
remove_filter('thesis_site_title', array($thesis->skin, 'logo'));
 
function my_logo($title) {
?>
<a href="http://mysite.com">
<img width="200" height="150" title="click to return home" alt="Grind T2 header image" src="http://mysite.com/header.jpg" id="thesis_header_image">
</a>
<?
}
add_filter('thesis_site_title', 'my_logo'); 

// STOP DON'T COPY ALL THIS INTO YOUR CUSTOM.PHP CHOOSE THE OPTION ABOVE OR BELOW THIS COMMENT.

// Use this if you want a text header
global $thesis;
remove_filter('thesis_site_title', array($thesis->skin, 'logo'));

function my_logo($title) { 
    ?>
    <h1 id="site_title">
    <a href="http://thesis.dev/grind">Grind &ndash; T2</a>
    </h1>
    <?
    }
add_filter('thesis_site_title', 'my_logo');