@Jonathan: Ok is this is not working for you then you can build child theme and create functions.php file and add the following code
<?php
/**
* Header Image
*
* Uses Custom Header and Featued Images
* @Hooked in catchevolution_headercontent
* @since Catch Evolution 1.0
*/
function catchevolution_featured_header() {
global $wp_query, $post, $paged, $_wp_default_headers;
// Header Image
$header_image_path = get_header_image();
// Check if this is a post or page, if it has a thumbnail, and if it's a big one
if ( is_singular() && current_theme_supports( 'post-thumbnails' ) &&
has_post_thumbnail( $post->ID ) &&
( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'post-thumbnail' ) ) &&
$image[1] >= HEADER_IMAGE_WIDTH ) :
// Houston, we have a new header image!
echo '<div id="header-image">';
echo get_the_post_thumbnail( $post->ID );
echo '</div>';
elseif ( get_header_image() ) : ?>
<div id="header-image">
<img src="<?php header_image(); ?>" width="<?php echo get_custom_header()->width; ?>" height="<?php echo get_custom_header()->height; ?>" alt="" />
</div>
<?php endif;
} // catchevolution_featured_header