invp_get_the_photos( mixed $sizes, int|null $post_ID = null )

	 * Backwards compatibility to versions before 5.4.0 where the
	 * incoming argument was a string not an array.
	 */
	if ( ! is_array( $sizes ) ) {
		$sizes = array( $sizes );
	}

	if ( empty( $post_ID ) ) {
		$post_ID = get_the_ID();
	}

	$images = get_posts(
		array(
			'meta_key'       => apply_filters( 'invp_prefix_meta_key', 'photo_number' ),
			'posts_per_page' => -1,
			'order'          => 'ASC',
			'orderby'        => 'meta_value_num',
			'post_mime_type' => 'image',
			'post_parent'    => $post_ID,
			'post_status'    => 'inherit',
			'post_type'      => 'attachment',
		)
	);

	// Did we find any photos?
	if ( empty( $images ) ) {
		/**
		 * No. Perhaps this vehicle has attachments, but they don't have our
		 * meta key. Just rely on the post date for sequencing.
		 */
		$images = get_posts(
			array(
				'posts_per_page' => -1,
				'order'          => 'ASC',
				'orderby'        => 'post_date',
				'post_mime_type' => 'image',
				'post_parent'    => $post_ID,
				'post_status'    => 'inherit',
				'post_type'      => 'attachment',
			)
		);
	}

	$image_urls = array();
	foreach ( $images as $image ) {
		foreach ( $sizes as $size ) {
			$img_element = wp_get_attachment_image(
				$image->ID,
				$size,
				false,
				array( 'class' => "attachment-$size size-$size invp-image" )
			);

			$image_urls[ $size ][] = $img_element;

			if ( 'large' === $size ) {
				$image_urls['urls'][] = INVP::extract_image_element_src( $img_element );
			}
		}
	}

	/**
	 * Backwards compatibility to versions before 5.4.0 where the
	 * incoming argument was a string not an array.
	 */
	if ( 1 === count( $sizes ) && 'large' !== $sizes[0] ) {
		return $image_urls[ $sizes[0] ];
	}

	return $image_urls;
}

/**