Insert Header Image in Thematic Child Theme

gistfile1.php

// sizing for custom header
// http://codex.wordpress.org/Custom_Headers
$headerargs = array(
    'flex-width'    => true,
    'width'         => 1140,
    'flex-height'    => true,
    'height'        => 250,
    'default-image' => get_stylesheet_directory_uri() . '/images/header.png',
);
add_theme_support( 'custom-header', $headerargs );

// add custom image to Thematic Child Theme inside the #branding div in the header
function childtheme_add_header_image() { ?> 
<img src="<?php header_image(); ?>" height="<?php echo get_custom_header()->height; ?>" width="<?php echo get_custom_header()->width; ?>" alt="" /> 
<?php }
add_action('thematic_header', 'childtheme_add_header_image', 6);