The folder for an album can be retrieved by the function `$album->getFolder()`.
The variable `$_zp_current_album` can usually be used, so `%_zp_current_album->getFolder()` will work in image.php and in album.php as long as you reference it before the `next_album()` loop. (That loop points `$zp_current_album` at each subalbum as you go through the loop.