get_the_post_thumbnail

Source code

function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $attr = '' ) {

	$post_id = ( null === $post_id ) ? get_the_ID() : $post_id;

	$post_thumbnail_id = get_post_thumbnail_id( $post_id );

	$size = apply_filters( 'post_thumbnail_size', $size );

	if ( $post_thumbnail_id ) {

		do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size ); // for "Just In Time" filtering of all of wp_get_attachment_image()'s filters

		if ( in_the_loop() )

			update_post_thumbnail_cache();

		$html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );

		do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );

	} else {

		$html = '';

	}

	return apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr );

}