* @since 4.4.0 `$post` can be a post ID or WP_Post object.

 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.

 * @return bool Whether the post has an image attached.

function has_post_thumbnail( $post = null ) {

	return (bool) get_post_thumbnail_id( $post );

 * Retrieve post thumbnail ID.

 * @since 4.4.0 `$post` can be a post ID or WP_Post object.

 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.

 * @return string|int Post thumbnail ID or empty string.

function get_post_thumbnail_id( $post = null ) {

	$post = get_post( $post );

	if ( ! $post ) {

		return '';

	}

	return get_post_meta( $post->ID, '_thumbnail_id', true );

 * @param string|array $size Optional. Image size to use. Accepts any valid image size, or

 *                           an array of width and height values in pixels (in that order).

 *                           Default 'post-thumbnail'.

 * Update cache for thumbnails in the current loop.

 * @global WP_Query $wp_query

 *

 * @param WP_Query $wp_query Optional. A WP_Query instance. Defaults to the $wp_query global.

 * @since 4.4.0 `$post` can be a post ID or WP_Post object.

 * @param int|WP_Post  $post Optional. Post ID or WP_Post object.  Default is global `$post`.

 * @param string|array $size Optional. Image size to use. Accepts any valid image size, or

 *                           an array of width and height values in pixels (in that order).

 *                           Default 'post-thumbnail'.

 * @return string The post thumbnail image tag.

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

	$post = get_post( $post );

	if ( ! $post ) {

		return '';

	}

	$post_thumbnail_id = get_post_thumbnail_id( $post );

	 * Filters the post thumbnail size.

	 * @since 4.9.0 Added the `$post_id` parameter.

	 * @param string|array $size    The post thumbnail size. Image size or array of width and height

	 *                              values (in that order). Default 'post-thumbnail'.

	 * @param int          $post_id The post ID.

	$size = apply_filters( 'post_thumbnail_size', $size, $post->ID );

		 * @param int          $post_id           The post ID.

		 * @param string       $post_thumbnail_id The post thumbnail ID.

		 * @param string|array $size              The post thumbnail size. Image size or array of width

		 *                                        and height values (in that order). Default 'post-thumbnail'.

		do_action( 'begin_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );

		 * @param int          $post_id           The post ID.

		 * @param string       $post_thumbnail_id The post thumbnail ID.

		 * @param string|array $size              The post thumbnail size. Image size or array of width

		 *                                        and height values (in that order). Default 'post-thumbnail'.

		do_action( 'end_fetch_post_thumbnail_html', $post->ID, $post_thumbnail_id, $size );

	 * Filters the post thumbnail HTML.

	 * @param string       $html              The post thumbnail HTML.

	 * @param int          $post_id           The post ID.

	 * @param string       $post_thumbnail_id The post thumbnail ID.

	 * @param string|array $size              The post thumbnail size. Image size or array of width and height

	 *                                        values (in that order). Default 'post-thumbnail'.

	 * @param string       $attr              Query string of attributes.

	return apply_filters( 'post_thumbnail_html', $html, $post->ID, $post_thumbnail_id, $size, $attr );

}

/**

 * Return the post thumbnail URL.

 *

 * @since 4.4.0

 *

 * @param int|WP_Post  $post Optional. Post ID or WP_Post object.  Default is global `$post`.

 * @param string|array $size Optional. Registered image size to retrieve the source for or a flat

 *                           array of height and width dimensions. Default 'post-thumbnail'.

 * @return string|false Post thumbnail URL or false if no URL is available.

 */

function get_the_post_thumbnail_url( $post = null, $size = 'post-thumbnail' ) {

	$post_thumbnail_id = get_post_thumbnail_id( $post );

	if ( ! $post_thumbnail_id ) {

		return false;

	}

	return wp_get_attachment_image_url( $post_thumbnail_id, $size );

}

/**

 * Display the post thumbnail URL.

 *

 * @since 4.4.0

 *

 * @param string|array $size Optional. Image size to use. Accepts any valid image size,

 *                           or an array of width and height values in pixels (in that order).

 *                           Default 'post-thumbnail'.

 */

function the_post_thumbnail_url( $size = 'post-thumbnail' ) {

	$url = get_the_post_thumbnail_url( null, $size );

	if ( $url ) {

		echo esc_url( $url );

	}

/**

 * Returns the post thumbnail caption.

 *

 * @since 4.6.0

 *

 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.

 * @return string Post thumbnail caption.

 */

function get_the_post_thumbnail_caption( $post = null ) {

	$post_thumbnail_id = get_post_thumbnail_id( $post );

	if ( ! $post_thumbnail_id ) {

		return '';

	}

	$caption = wp_get_attachment_caption( $post_thumbnail_id );

	if ( ! $caption ) {

		$caption = '';

	}

	return $caption;

}

/**

 * Displays the post thumbnail caption.

 *

 * @since 4.6.0

 *

 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.

 */

function the_post_thumbnail_caption( $post = null ) {

	/**

	 * Filters the displayed post thumbnail caption.

	 *

	 * @since 4.6.0

	 *

	 * @param string $caption Caption for the given attachment.

	 */

	echo apply_filters( 'the_post_thumbnail_caption', get_the_post_thumbnail_caption( $post ) );

}