Thematic Theme Add Logo Image to Header

gistfile1.php

function childtheme_override_blogtitle() {
?>
    <div id="blog-title" class="site-title">
        <span>
            <a href="<?php echo home_url() ?>/" title="<?php bloginfo('name') ?>" rel="home">
                <img src="http://placekitten.com/300/150">
            </a>
        </span>
    </div>

<?php
}
add_action( 'thematic_header','thematic_blogtitle', 3 );