The Princess of Sales

Kirsty Wigglesworth / AP

LOOKING ON: A visitor views the work by Hiroshi Sugimoto of Diana, Princess of Wales on display at Sotheby's auction rooms in London.

Diana, Princess of Wales, was a commodity — and she had a pretty shrewd idea of her own value. "You see yourself as a good product that sits on a shelf and sells well," she said in a famous confessional BBC TV interview in 1995. "And people make a lot of money out of you."

They still do. When she was alive, everyone wanted a piece of Diana. Photographers chased after her smile, newspapers hung on her words, her fans bought anything that would get them that little bit closer to the fairy tale. And...