function invp_get_the_photos( $sizes, $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 ( ! in_array( 'full', $sizes, true ) ) {
		$sizes[] = 'full';
	}

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

	// Use the object cache instead of transients to avoid MySQL deadlocks when
	// concurrent requests for the same vehicle all miss the cache simultaneously
	// and race to write the same options table row.
	$cache_group      = 'invp_photos';
	$cache_key_images = 'images_' . $post_ID;
	$images           = wp_cache_get( $cache_key_images, $cache_group );
	if ( false === $images ) {
		$images = get_posts(
			array(
				'meta_key'       => apply_filters( 'invp_prefix_meta_key', 'photo_number' ),
				'posts_per_page' => apply_filters( 'invp_query_limit', 1000, __FUNCTION__ ),
				'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' => apply_filters( 'invp_query_limit', 1000, __FUNCTION__ ),
				'order'          => 'ASC',
				'orderby'        => 'post_date',
				'post_mime_type' => 'image',
				'post_parent'    => $post_ID,
				'post_status'    => 'inherit',
				'post_type'      => 'attachment',
			)
		);
	}

	if ( ! empty( $images ) ) {
		wp_cache_set( $cache_key_images, $images, $cache_group, MINUTE_IN_SECONDS * 5 );
	}

	$cache_key_image_urls = 'image_urls_' . $post_ID;
	$image_urls           = wp_cache_get( $cache_key_image_urls, $cache_group );
	if ( false === $image_urls ) {
		$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" )
				);

				if ( '' === $img_element ) {
					continue;
				}

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

				if ( 'full' === $size ) {
					$image_urls['urls'][] = INVP::extract_image_element_src( $img_element );
				}
			}
		}
		wp_cache_set( $cache_key_image_urls, $image_urls, $cache_group, MINUTE_IN_SECONDS * 5 );
	}

	return $image_urls;
}