<?php
// ALL parameters are optional. Not needed if you are on WP LOOP
echo get_the_post_thumbnail_url( $the_query->ID, array( 500, 400) ); ?>
<img src='<?php the_post_thumbnail_url(); ?>'>
<?php if (has_post_thumbnail( $post->ID ) ): ?>
<?php $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'single-post-thumbnail' ); ?>
<div id="custom-bg" style="background-image: url('<?php echo $image[0]; ?>')">
</div>
<?php endif; ?>
$img_url = wp_get_attachment_image_url(get_post_thumbnail_id(get_the_ID()), 'full');
<img src="<?PHP echo $img_url?> ">