All of the images from an album are stored in a single directory... so you can use a recursive delete function to delete all of the files and folders in that directory...
Here is a function you can use to delete a directory and all of its contents:
function deleteDirectory($dir) {
if (!file_exists($dir)) return true;
if (!is_dir($dir) || is_link($dir)) return unlink($dir);
foreach (scandir($dir) as $item) {
if ($item == '.' || $item == '..') continue;
if (!deleteDirectory($dir . "/" . $item)) {
chmod($dir . "/" . $item, 0777);
deleteDirectory($dir . "/" . $item);
};
}
return rmdir($dir);
}