We once bought a "stock" photo of a nice living room to use in a brochure. Turned out the photographer sold the photo and never got permission from the homeowner. The living room happened to belong to a customer of ours, and we were fortunate to keep the customer and dump a lot of brochures in the recycle bin. (A friend in the biz used pictures from a home without permission and lost the customer.) I doubt this happens much with stock photo firms, but since we no longer use any stock photos we're careful about how and when pictures are taken. Permission in writing is critical if you take pictures for use in public that can be identified with anyone's building or belongings.
If you go for stock, just avoid using the pics of guys in short sleeve shirts and ties. 8)