It is perhaps the most reproduced, recycled and ripped off image of the 20th Century. Che Guevara, his eyes framed by heavy brows, a single-starred beret pulled over his unruly hair, stares out of the shot with glowering intensity. It's now more than 50 years since the Argentine-born rebel was shot dead, so any young radicals who cheered on his revolutionary struggles in Cuba and Bolivia are well into middle age.
But the image has been infinitely repeated - emblazoned on T-shirts and sprayed on to walls, transformed into pop art and used to wrap ice-creams and sell cigarettes - and its appeal has not faded. "There is no other image like it. What other image has been sustained in this way?" asks Trisha Ziff, the curator of a touring exhibition on the iconography of Che. "Che Guevara has become a brand. And the brand's logo is the image, which represents change. It has becomes the icon of the outside thinker, at whatever level - whether it is anti-war, pro-green or anti-globalisation," she says.
The unchecked proliferation of the picture - based on a photograph by Alberto Korda in 1960 - is partly due to a political choice by Korda and others not to demand payment for non-commercial use of the image. Jim Fitzpatrick, who produced the ubiquitous high-contrast drawing in the late 1960s as a young graphic artist, said he actively wanted his art to be disseminated.
"I deliberately designed it to breed like rabbits," he says of his image, which removes the original photograph's shadows and volume to create a stark and emblematic graphic portrait. "I was determined that the image should receive the broadest possible circulation," he adds.
For Ms Ziff, Che Guevara's murder also marks the beginning of the mythical image. "The birth of the image happens at the death of Che in October 1967," she says. "He was good-looking, he was young, but more than that, he died for his ideals, so he automatically becomes an icon."
The story of the original photograph, of how it left Cuba and was carried by admirers to Europe before being reinterpreted in Mr Fitzpatrick's iconic drawing, is a fascinating journey in its own right. Alberto Korda captured his famous frame on 5 March 1960 during a mass funeral in Havana. A day earlier, a French cargo ship loaded with ammunition had exploded in the city's harbour, killing some 80 Cubans - an act Fidel Castro blamed on the US. Korda, Fidel Castro's official photographer, describes Che's expression in the picture, which he labelled "Guerrillero Heroico" (the heroic fighter), as "encabronadao y dolente" - angry and sad. Unpublished, the picture was seen only by those who passed through Korda's studio, where it hung on a wall.
One man who brought the image to Europe was the leftist Italian intellectual, Giangiacomo Feltrinelli, who distributed posters across Italy in 1967. After that, Korda's photograph made an appearance in several European magazines. Mr Fitzpatrick first came across a tiny version of it in the German weekly. Only months later, when he finally got his hands on a larger version of the photograph, was he able to produce the image that has such universal appeal. "I'd got an original copy of the image sent to me by a guy involved with a group of Dutch anarchists, called the Provo."
After Che Guevara's death, an outraged Mr Fitzpatrick furiously reprinted originals of the poster and sent it to left-wing political activist groups across Europe. Part of his fury stemmed from vivid memories working behind a bar in Ireland as a teenager, and seeing Che walk in. The revolutionary was briefly exploring the homeland of his Irish ancestors during a stopover on a flight to Moscow. "I must have been around 16," Mr Fitzpatrick remembers. "It was a bright, sunny morning. I knew immediately who he was. He was an immensely charming man - likeable, roguish, good fun and very proud of being Irish."
Mr Fitzpatrick's version of Che arrived on the continent as many countries were in a state of flux, says Ms Ziff. "His death was followed by demonstrations, first in Milan and then elsewhere. Very soon afterwards there was the Prague Spring and May '68 in France. Europe was in turmoil. People wanted change, disruption and rebellion and he became a symbol of that change."
As time went on, the meaning and the man represented by the image became separated in the western context, Ms Ziff explains. But in Latin America, she points out, Che Guevara's face remains a symbol of armed revolution and indigenous struggle. Combining capitalism and commerce, religion and revolution, the icon remains unchallenged, Ms Ziff says. "There is no other image that remotely takes us to all these different places."