attachment_url_to_postid( string $url )

function attachment_url_to_postid( $url ) {
	global $wpdb;

	$dir = wp_get_upload_dir();
	$path = $url;

	$site_url = parse_url( $dir['url'] );
	$image_path = parse_url( $path );

	//force the protocols to match if needed
	if ( isset( $image_path['scheme'] ) && ( $image_path['scheme'] !== $site_url['scheme'] ) ) {
		$path = str_replace( $image_path['scheme'], $site_url['scheme'], $path );
	}

	if ( 0 === strpos( $path, $dir['baseurl'] . '/' ) ) {
		$path = substr( $path, strlen( $dir['baseurl'] . '/' ) );
	}

	$sql = $wpdb->prepare(
		"SELECT post_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attached_file' AND meta_value = %s",
		$path
	);
	$post_id = $wpdb->get_var( $sql );

	/**
	 * Filters an attachment id found by URL.
	 *
	 * @since WP-4.2.0
	 *
	 * @param int|null $post_id The post_id (if any) found by the function.
	 * @param string   $url     The URL being looked up.
	 */
	return (int) apply_filters( 'attachment_url_to_postid', $post_id, $url );
}