$thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'large' ); code example
Example 1: wp+get feature image
<?php
echo get_the_post_thumbnail( $post_id, 'thumbnail' );
?>
Example 2: wordpress get post thumbnail
<?php
/* RETURNS a full image resource as: <img class="data..." src="data...">
ALL parameters are optional. Not needed if you are on WP LOOP
*/
echo get_the_post_thumbnail( $the_query->ID, array( 500, 400) );
/* USE get_the_post_thumbnail_url() to get only the image url */
?>