Add full size background image to thematic

function kia_add_bg_image(){ ?>

<!--BACKGROUND IMG-->
<div id="bg">
<img src="http://www.fionaurora.com/rrwp/wp-content/themes/rrtheme/img/catdog7_bg.jpg"/></div>

<?php }
add_action('thematic_before','kia_add_bg_image');