Featured image of Parent page

new_gist_file

<?php global $post;
if (isset($post)) {
    
    //get the ancestors
    $familyTree = get_ancestors($post->ID,'page');
    array_unshift( $familyTree, $post->ID ); //add the current page to the begining of the list
    
    //loop through the family tree until you find a result or exhaust the array
    $featuredImage = '';
    foreach ( $familyTree as $family_postid ) {
        if ( has_post_thumbnail( $family_postid ) ) {
            $featuredImage = get_the_post_thumbnail( $family_postid, 'full' );
            break;
        }
    }
    
    // if the page has a featured image then show it
    echo ( $featuredImage ? $featuredImage : "" );
 
}?>