Drupal 7 Snippet: Select a header image based on the topmost active menu item

mytheme_get_headerimage.php

/**
 * Return header image based on the node id of the topmost active menu item
 * @return Absolute path to the image selected
 */
function get_header_image() {
	// Get the Page's Parent Menu Item
	$menuParent = menu_get_active_trail();

        // background images based on node id's
	$node_imgs = array(
		8 => 'header1.jpg',
		12 => 'header2.jpg',
		25 => 'header3.jpg',
	);

	$header = 'default_header.jpg';

        // Get the topmost menu element
	if (!empty($menuParent[1])) {
		$linkpath = $menuParent[1]['link_path'];

		if (!empty($linkpath)) {
                        // search for node id in it's link_path
			preg_match("/node\/(\d+)/i", $linkpath, $match);
			if (!empty($match) && !empty($node_imgs[$match[1]]))
				$header = $node_imgs[$match[1]];
		}

	}
        // return absolute path to the
	return base_path() . drupal_get_path('theme', 'MY_THEME_NAME') . '/images/header/' . $image;
}