how to get the image of a post wordpress code example

Example 1: 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 */
?>

Example 2: show featured image in post wordpress

<?php if(has_post_thumbnail()){
  the_post_thumnbail('cstm_name', array( 'class' => 'class1 class2' ))
} else { ?>
  <img class="card-img-top" src="http://placehold.it/750x300" alt="Card image cap" class="img-responsive">
<?php } ?>