That said, there are strong similarities between British and U.S. copyright laws based on our common origins. Under U.S. copyright law, absent a written agreement to the contrary, the copyright in a photograph is owned either by the photographer or, if employed to take the photos, the photographer's employer. If there is a written agreement regarding the photographs, that will control what you can do. As you may recall from our previous blog, you are free to take and use photographs of publicly viewable buildings. Those rules do not apply to interior architecture.
Which leads to the other wild card issue -- the content of the pictures. There may be architectural or artistic elements in the photos that are protected under copyright and would require permission -- say, for example, a uniquely designed kitchen or a Henry Moore statue. Finally, persons dwelling in those apartments may have privacy rights and you could run into problems selling intrusive photos -- for example, images that reveal personal photographs, bondage handcuffs, or empty bottles of Wild Turkey.