WordPress Quick Get Featured Image by Post ID

/* 
 * $this could be attachment ID, $post, or whatever post object you are looping.
 * 'large' is the sized format - change to desired size (medium, large, thumbnail etc)
 * Returns array(URL, width, height, alt_text)
 */

$image = wp_get_attachment_image_src( get_post_thumbnail_id( $this->ID ), 'large' );