$users_query = mysql_query("select * from likes l join users u where l.user_id = u.id
and l.photo_id = '$photo_id' LIMIT 6");
$users_query = mysql_query("select * from likes l join users u where l.user_id = u.id
and l.photo_id = '$photo_id'");
$num_users_likes = mysql_num_rows($users_query);