Robert Fisk’s World: The right photographer can strip a leader's power in a flash

Karsh was an arch man, not afraid to make his sitter into a clown or a chump

The photograph was taken in the Speaker's Chamber in the Canadian House of Commons in Ottawa – only a four-hour train ride down the old Canadian Pacific tracks from the studio in Toronto where Shelton Chen is displaying it now – and Churchill had just delivered his "Some chicken – some neck!" speech to a crescendo of applause.

But it wasn't the speech that made him glower. Nor was it Hitler's apparently imminent capture of Moscow. Churchill was a sick man when he arrived in Ottawa, "flabby and tired" according to the Canadian prime minister, Mackenzie King. But no, it wasn't his health. It was the little problem of his cigar.

Churchill did not know that King had trapped him into the photo session and grudgingly told Karsh – a Turkish-Armenian whose father saved his family from the Armenian genocide in 1915 through his friendship with a Turkish army commander – that he could take only one picture. Churchill's Havana cigar was between his lips but Karsh didn't want a portrait that included this old theatrical prop. So he plucked it from the old boy's mouth with the words: "Sir, I have an ashtray all prepared for you." By the time he got back to his camera, Karsh was to recall, "He looked so belligerent he could have devoured me." Bingo. Lion at bay.

So I look at the photograph again. Churchill thwarted. Churchill not a little insulted. His hair, I notice suddenly, is soft and parted in such a central way that it almost covers his baldness. And his hands. In Karsh's picture, they are smooth, almost feminine, but the jowls are heavy, not a man to suffer fools, especially when they steal his cigar. But as I glance to the right, there is a different Churchill.

As Maria Tippett was to write in her warm biography of Karsh, the Canadian parliament speaker was lighting another cigar and Churchill brightened at once, offering Karsh one more shot. The insult had turned into admiration for the Armenian's pluck. "Well, you certainly can make a roaring lion stand still to photograph him," Churchill growled. And there is the second Churchill on the studio wall beside me, benevolent, generous, eyes ablaze, a happy poseur glorying in publicity, lion turned labrador-golden retriever at bay.

Back in his developing room, Karsh realised he had captured an inspiring moment. But, as Tippett writes, "Much had to be done during the washing, drying, retouching, and other stages of the developing and printing process. He had to make Churchill look less tired and less haggard... He had to give Churchill more strength and gravitas by giving him more solidity." And he had to give more strength – not very successfully, it has to be said – to those feminine hands which, Karsh himself admitted, had shocked him. "Middle tones" were added to the prime minister's face. Churchill was now almost superhuman. Who would imagine that Singapore was about to fall, that there might be U-boats waiting for him in the Atlantic on his way home?

So is the photograph "real"? Is this Churchill? Or a Karsh version of Churchill? Karsh was an arch man, not afraid to make his sitter into a clown or a chump. I looked carefully at his 1963 portrait of Khrushchev – taken only months before he was deposed – and the Armenian had persuaded the First Secretary of the Communist Party of the Soviet Union and Lord of all the Russias to wear a heavy fur coat and knitted hat. He beams out of it, all charm and humour and spotty face. "Be quick, it's very warm," Nikita told Karsh, "and this is a ferocious animal. It is likely to eat me up." But is this the Khrushchev who would be eaten up by the Politburo the following year, the man who banged his shoe on the table at the United Nations, the former political commissar in the ruins of 1942 Stalingrad? Or a Karsh creation? (He also got Khrushchev to pose with his arm in the air as if saluting troops.)

The other portraits ask questions of themselves. Did Gregory Peck really have such a giant quiff – this was in 1946 – and did Brigitte Bardot really wear so much make-up in 1958 (probably yes) and was Ingrid Bergman so happy in 1946? Laurence Olivier is holding a glass of white wine – poured by Karsh, perhaps? – while a vast colour portrait of Charlton Heston shows the awful hypocrite resting his hand on a volume of Thomas Mann. In 1956, Yul Brynner looks appropriately mysterious; G B Shaw's eyes peer from below his massive, shadowing eyebrows in 1943. But surely that is only because Karsh's lights were set close above the left side of his head. Yes, it's all about light – that's how God blesses Karsh's subjects.

Poor old Jean Sibelius (1949) has skin like delicate parchment, but Karsh has told him to close his eyes – prominent Finnish composer dreams of the Karelia Suite, I suppose – while an uncompromising Admiral Mountbatten in uniform (1943) looks past us with boundless arrogance. Did Madame Chiang Kai-Shek always wear a veil? Hemingway (1947) looks like the drinker he was, but were his eyes actually suspicious? Castro, hands on hips, challenging, accusatory, angry eyes – this was in 1971 – looks like the kind of man whose anger will embrace a photographer or two.

I suspect, in the end, that we have to accept that portraiture is art. We have to take the dictators and fools and rogues and heroes at Karsh's version of face value but not, I suspect, as vérité, not necessarily the man we would have seen in the Ottawa speaker's chambers or in Khrushchev's dacha or in Heston's favourite hotel in Beverly Hills. Yes, I would like to know just how sick Churchill really was in 1941 (and later) but so would the rest of the world, including the leader of Nazi Germany.

Which raises another question. If Hitler had smoked, what would have happened to Karsh had he plucked a cigar from the Führer's lips?