Yet, whenever painters stepped into the ring, commissioned to create something that would be more than just a temporal or documentary record of celebrity, they were met with growls of general criticism.
Their portraits were judged either too glib, too sugary or too cruel. And this despite the fact that several of the painters for whom the Princess sat continue to regard her as one of the warmest and most helpful of subjects.
"She was a delight and absolutely co-operative," recalls June Mendoza, the celebrated portrait artist who has also painted the Queen, the Queen Mother and Princess Anne. "Mine was a fairly romantic painting, but that was because she was a young, slim, beautiful girl."
Mendoza had been commissioned by a London livery company to paint Diana in a red evening dress during the early stages of her second pregnancy.
"There were no marks of age on her face then, although she told me she was already being hounded and was facing an enormous amount of change in her life," she said.
"Some of the pictures that followed mine have over-romanticised her, I think, and are a little bit icky. I would love to have painted her again, as she became a more rounded person."
The late Princess seems to have been equally accommodating when it came to less established portraitists.
The painter Israel Zohar treasured his sketching sessions with Diana, held at Kensington Palace seven years ago. "She seemed so different to the distant way I had imagined her," he says.
Nervous at the beginning, he had asked just how close he was allowed to sit. "She said to me: 'As long as you don't sit in my lap I think it will be all right...' I almost forgot that I was with this person who was so famous. But I remember looking into her eyes and seeing that she was not happy at all."
Perhaps the strongest and one of the most controversial paintings of Diana in recent years was commissioned by the Red Cross and painted by Henry Mee.
The painter says he found the Princess hugely helpful, although profoundly troubled. "When I painted her in 1995, it was clearly a very difficult phase in her life. She spoke at length about her feeling of being hounded by photographers. She was absolutely raw about the divorce and very upset about the photographs which had just been secretly taken from the ceiling of a gym.
"She told me she hated having cameras pointed at her. She was clearly under immense stress. The reality was that she felt imprisoned in a central London flat."
Given access to her whole wardrobe, Mee chose the modern, dark blue evening dress she had worn to great effect in New York. He had previously painted the Queen in a style which he hoped would be read as iconic, but with Diana he wanted to show the relatively unfamiliar image of a grown-up princess
The other equally contentious artist's interpretation of the Princess, David Hankinson's 1992 portrait, was widely criticised for being too soppy, rather than too harsh. A swirl of fairytale ballgown in pink and blue, it was dubbed "a kind of death by portrait" by Marina Vaizey, art critic for the National Art Collections Fund.
The painter Douglas Anderson was also attacked for giving his portrait a pretty-pretty effect, while John Merton's three-headed study was called tasteless.
Richard Foster's 1986 picture was criticised as ugly, although the artist described it as wistful.
One the most recent official portraits of Diana was painted by an American, Nelson Shanks, for whom she sat in 1994.
Probably the most admired painting of Diana is Bryan Organ's 1981 engagement commission, housed in the National Portrait gallery and restored after a student slashed the canvas in protest over Ireland.
This week, Organ's picture of the teenage bride-to-be has never looked more pathetic, yet it is perhaps more poignant still to contemplate the details of a portrait that will now never be.
Royal painter Michael Noakes had always hoped to be commissioned to portray Diana in a more unconventional manner. "I had a definite idea about how I would do it and I am terribly sad that I did not have the chance," he said.
Will any of the completed portraits of Diana ever compete with the apparent intimacy of the photo-shoot? Will theirs be images that remain? The passing decades will tell us.