Overcast skies made for an unseasonably cold day in Havana on May 5, 1960. Thousands were assembled to memorialize those killed in an explosion in the city’s harbor the day before. Barely a year after the Cuban revolution, Fidel Castro passionately spoke to the crowd. As he spoke, the “second face” of the uprising briefly came into view. Ernesto “Che” Guevara appeared and scanned the crowd with a steely determination. Cuban photographer Alberto Díaz Gutiérrez, known as Korda, was able to capture only two photos of the famed Che before he receded from view.

The first frame has become the most widely circulated photograph in history, as ironic as it is ubiquitous. It is a testament to the power of image.

I spent roughly half of my career in photojournalism, first as a shooter, then supervising photographers and their work. At a quick first glance, the familiar, cropped version of the photo might pass for a studio portrait, using classic “three-quarter” light — known for its flattery. The overcast light of that day was soft, kind to the moment. On closer inspection, the photo is clearly a captured image — gritty, fleeting, overwhelmed by Che’s eyes that portray anger, sadness, resolution or whatever we wish to read into them.

The photograph and the man have become, says author Michael Casey, “anything to anyone and everything to everyone.”

Casey’s book, Che’s Afterlife: The Legacy of an Image, traces the life of the photograph from Korda’s Leica camera, through a few years of obscurity — the image was actually passed over by his editors in coverage of the state memorial service — to iconic status stamping cool onto everything from dorm room posters to T-shirts to coffee mugs to condoms. The image even made it to the world of high fashion, carried to the catwalk on a skimpy bikini worn by supermodel Gisele Bundchen. Irony abounds. Che hated crass American commercialism almost more than anything. And Che knew about hate.

In the introduction to his book, Casey recounts a 2007 festival in Buenos Aires celebrating Argentina’s 1976 coup. The “Guerrillero Heroico” image, as it’s now known, was everywhere. No surprise, since Che was born in Argentina. Casey asked a flag salesman whether he liked Che personally. “Yes,” the man replied. “He sells well.”

No one looks equally good in every light. Photographers know this, sometimes even to our own disadvantage.

The public imagination knows almost nothing of the man behind the cult of Che, other than that he’s cool and he sells well.

Indeed, there may be no way to gain an objective measure of the man. Cyberspace has become a cage match where hagiographers and detractors swap endless anecdotal blows. A selfless freedom fighter. A relentless self-promoter. Ideologically pure. Ideologically ruthless.

Yet a few things rise above the noise.

Born in Argentina, Che became a physician, or at least studied medicine, and then left to join the revolutionary movements in Latin America. He became second-in-command of Fidel’s revolution. After victory, he was put in charge of Cuba’s first firing squads and so became responsible for the deaths of dozens, hundreds, thousands — your mileage may vary. At least a few of those were at his own hand, which his writings describe with unvarnished affection. “Hatred is an element of struggle,” he later wrote, “unbending hatred for the enemy, which pushes a human being beyond his natural limitations, making him into an effective, violent, selective, and cold-blooded killing machine. This is what our soldiers must become.”

Originally a big fan of the Soviet Union, Che became disenchanted after the 1962 Cuban Missile Crisis. Why? He was furious when they backed down; he considered a nuclear war that would have killed untold millions a worthy cost in the struggle against imperialism.

The life of a post-revolution bureaucrat didn’t suit him, so in 1965 Che left Cuba to lead revolutions in the Congo and then Bolivia — both spectacular failures. He was caught and executed by Bolivian solders in 1967.

On the other hand, he’s cool and he sells well.

The strange journey of the “Guerrillero Heroico” photo is as much a story of the power of marketing as anything. But as a photographer, I’m convinced the image would not have become such a phenomenon had May 5th been a typical cloudless Caribbean day. Harsh shadows and squinty eyes don’t make for an enduring icon. The lighting was, as philosophers like to say, necessary but not sufficient.

Most people have no idea of the power of the atmospherics of an image. Here’s a test: Next time you watch a movie, forget the movie itself. Watch the lighting. Wherever possible, outdoor shots will take place in the “golden hour” either after sunrise or before sunset. The alpha male will often be given Che-like three-quarter light. The lead actress will generally be rendered in soft backlight. Multiple people appearing together in an outdoor shot will always be backlit.

No one looks equally good in every light. Photographers know this, sometimes even to our own disadvantage.

At our senior prom many years ago, my date and I stepped away from the sweaty ballroom for a brief romantic encounter. Standing alone on a patio overlooking downtown Phoenix, I caressed her shoulder and proceeded to gently move her over a couple of feet.

“There you go,” I said innocently — or rather, cluelessly. “You look better in this light.”

The moment took a sharply less romantic turn. Still, I hoped she would forgive me. The prom date is now my wife; 35 years later, I’m still hoping.

After all, what works for a communist revolutionary ought to work for a prom date.