The Digital Collection of the Museum of the City of New York includes more than one hundred photographs of St. Luke's Hospital. The images document both the exterior and the interior spaces. The photographs of the interior spaces are exceptional and include the various pavilions: Muhlenberg, Vanderbilt, and Norris. There are images of the ambulance house, autopsy room, laundry, and dining areas, among other spaces. The collection also includes several postcards.
New York Public Library Digital Collections also includes more than thirty images of St. Luke's Hospital, primarily exterior shots.
The Seymour Durst Collection at Columbia University includes photographs of St. Luke's with a good collection of postcards.
Google Images is useful for more contemporary images of St. Luke's Hospital.