When visitors first arrived they were seated in a Chippendale chair and told to remain still until Mumler's wife Hannah, a clairvoyant medium, had summoned the spirits. Although it often took several attempts before a ghost image was developed, customers always left "fully satisfied that the pictures were what they claimed to be--real photographs of real spirits".
The above engravings from the Haunted Historian collection are a rare look inside Mumler's studio.
Source: Kaplan, Louis. The Strange Case of William Mumler, Spirit Photographer. (2008)