Change Thematic Blog Title to Logo or Image

gistfile1.php

// replace the site title text with an image that links back to homepage, usually for logos
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/100/100" alt="<?php bloginfo('name') ?>" />
            </a>
        </span>
    </div>
<?php
}