Three young students listen to a teacher describing Giovanni Paolo Pannini's painting of the interior of Saint Peter's, Rome.  A young man and a woman have walked up to hear to his talk. 

Other women are discussing the neighboring Canaletto's painting of the Piazzetta, Venice, and Luca Carlevarijs' painting of the Molo, Venice.

 All these early 18th century paintings are hanging in a gallery at the Norton Simon Museum, in Pasadena, California. The painting is composed from photographic images captured while visiting the museum.