Phillygirl:
We have done our last two renewals at our local county service center. At that location they did both the renewal and photos. The cost of the photo was actually less than the cost at Wal-Mart and they know immediately that it will be accepted. It is also much faster and convenient.
You can find a location that has photo service on site by clicking on this link and putting in your zip code:
Where to Apply For A Passport
Take care,
Mike