Add featured image to a WordPress page

header.php

<?php
/** 
* Themes must declare support for the Featured Image function before 
* the Featured Image interface will appear on the Edit screen.
* add_theme_support( 'post-thumbnails' );
* https://developer.wordpress.org/themes/functionality/featured-images-post-thumbnails/ 
*/
?>
<?php if (has_post_thumbnail()): 
	$image_url = wp_get_attachment_image_src( get_post_thumbnail_id());
		// add custom attached image here
	else:  
		// default image
	endif;
?>	


/**
 *   the_title(); will display the title of the first post on a custom blog page.
 *   either option below will display the title of the custom page.
 **/
 
<?php echo apply_filters('the_title',get_page( get_option('page_for_posts') )->post_title); ?>

// Or

<?php echo single_post_title(); ?>