Give me the description of the service type that offers not only the photo product but also the film product.
select t1.service_type_description from ref_service_types as t1 join services as t2 on t1.service_type_code = t2.service_type_code where t2.product_name = 'photo' intersect select t1.service_type_description from ref_service_types as t1 join services as t2 on t1.service_type_code = t2.service_type_code where t2.product_name = 'film'