You should have a field in your database called something along the lines of, "approved". The values should be either '0', waiting for approval, or '1', for approved. That way, when you display the gallery you can include this condition in your query to only display the photos that have been approved.
As for listing the queued photos, you can do the opposite. You can list all of the photos in the queue with a '0' for the "approved" column along with a corresponding checkbox. When you submit this page it should iterate through all of the checked photos and update the database to have these photos approved (1).
Do you have any of this page setup yet?