Another common example of a two-level bidirectional supply chain is professional photography. Often, professional photographers do not process exposed film themselves, but instead send the film to a film processing company. The supply chain is as follows: customers provide their subjects (themselves, their kids, etc.) to the photographer who records them on film which is supplied to the film processing company. Therefore the end customer is a second-tier supplier to the film processing company. The film processing company supplies completed prints back to the photographer, who makes them available to the end customer. Therefore, the film processor is a second-tiersupplier to the end customer. By providing the subjects to be photographed, and by receiving the finished prints, the end customers are in fact fourth-tier suppliers to themselves! This and other examples of two-level bidirectional supply chains are shownin Figure2.