Subject the place WP Featured Picture is not going to show

The code I am utilizing, is exterior of WordPress i.e.

outline('WP_USE_THEMES', false);
require('weblog/wp-blog-header.php');    
world $wpdb;

The code that I am making an attempt to show the put up thumbnail (the set featured picture) is:

if(has_post_thumbnail($post->ID)){
    echo "has a thumb";
    get_the_post_thumbnail();
    the_post_thumbnail();
    the_post_thumbnail('medium');
    wp_get_attachment_image_src(get_post_thumbnail_id());
    wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ));
} else {
    echo "no thumb";
}

Now it does does accurately show if there’s a thumb or not, however would not return the thumb file title or something in any respect. I’ve tried all strategies I might discover and nothing is returned, neither is there any errors returned.

Recommendations, ideas?