Rockwell used photos, taken by a rotating cast of photographers, to make his illustrations... Rockwell never kept it a secret, but for some reason this little fact has been neglected in recent decades. Although he may not have clicked the shutter, Rockwell directed every facet of every composition.
A newly published book, Norman Rockwell: Behind the Camera (Little, Brown and Company, 2009), and an exhibition at the Norman Rockwell Museum provide further insight into this process and offer acknowledgement to the photographers involved in the process.
Those who feel the lack of freehand drawing somehow diminishes Rockwell's status as an artist should be reminded that painters as famous as Vermeer and Caravaggio are thought to have used the camera obscura to compose their works.
NPR link, via Photo District News, via (ovo). Photo credit Norman Rockwell Museum.
The person who commented on Rockwell's "tracing techniques" was Clemens Kalischer, an artist-photographer who reportedly "assisted Rockwell through the years."
...So let us please stick to the produce of mr. Norman Rockwell...