The image was stark _ a silent, solitary figure standing in passive defiance to the Turkish prime minister's demand for protesters to clear Taksim Square in central Istanbul.

The challenge by performance artist Erdem Gunduz is catching on with other protesters in Turkey, encouraged by social media into imitating his gesture across the country.

It's too early to tell whether the "standing man" protests will make a difference in the weeks-long challenge to the authority of Prime Minister Recep Tayyip Erdogan.

But singular actions, captured in images distributed around the world, have sometimes influenced the course of history and transformed obscure figures into symbols of their era.

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DEATH IN TEHRAN

Neda Agha-Soltan was a 26-year-old aspiring musician when she and her music teacher were driving to a protest rally in Tehran on June 20, 2009. The rally was one of many protests against the results of that year's presidential election, which the opposition said was rigged by supporters of President Mahmoud Ahmadinejad.

The car's air-conditioner wasn't working so she left the vehicle to continue on foot, stopping to watch a protest some distance from the main rally. Suddenly, a bullet allegedly fired by a pro-government militiaman pierced her chest.

As amateur video captured the scene, the young woman fell to the ground. She died within minutes. The video went viral and within hours Neda became the symbol of the struggle against Ahmadinejad and the cleric-run Islamic republic.

Eventually, the government gained the upper hand, and Ahmadinejad served out his second term. But the images kept her memory alive. As Iranians celebrated the victory of reformist-backed Hasan Rowhani in last week's election, some in the crowd yelled "it's the spring of freedom, too bad Neda isn't here."

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TANKS AT TIANAMEN SQUARE

There was no such name recognition for the "tank man," an anonymous figure who stood in front of a column of Chinese tanks on June 5, 1989, a day after Chinese troops forcibly removed pro-democracy protesters from Beijing's Tiananmen Square.

Had it not been for teams of photographers and video journalists perched on the roof of a nearby hotel, that personal act of defiance in the face of overwhelming power would have passed without notice.

As cameras rolled and shutters snapped, the man, whose face wasn't clearly visible in the distance, placed himself in front of the column of tanks, forcing them to stop.

Moments later, with the column halted, the man jumped on one of the vehicles, made his way to the turret and appeared to talk to the commander. Finally, video showed two figures in blue clothing pull the man away. All three disappeared into the crowd. To this day, Chinese authorities haven't identified the man nor given any indication what happened to him. Still, his actions live on in the image, an iconic symbol of one man's defiance.

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BUDDHIST MONK'S SELF-IMMOLATION

Few had ever heard of Thich Quang Duc before June 10, 1963, when a small group of journalists gathered on a street in South Vietnam's capital, Saigon, having heard that "something important" would happen.

Suddenly, hundreds of Buddhist monks appeared carrying banners denouncing repression of the Buddhist majority by the Catholic-dominated government of Prime Minister Ngo Dinh Diem.

The procession stopped.

Duc, one of the monks, took a seat on a cushion placed on the pavement. As a colleague poured gasoline on his head, Duc recited Buddhist prayers, struck a match and set himself on fire.

A photo by Associated Press journalist Malcolm Browne captured the moment and spread shock and horror around the world. The image destroyed claims by the U.S. and the South Vietnamese that the Buddhist protests were fizzling out.

On the other side of the globe, a stunned President John F. Kennedy said no news photo in history "has generated so much emotion around the world as that one." The image stirred a Buddhist rebellion in South Vietnam, already racked by war with the communist Viet Cong.

That uprising in turn destroyed support for Diem in the U.S., his chief backer. Five months later, Diem was slain in a military coup that toppled his government.

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KENT STATE MASSACRE

Mary Ann Vecchio wasn't even a student at Kent State University when she joined a protest at the Ohio campus against the Vietnam War on May 4, 1970.

She was a 14-year-old runaway from Florida. Yet the image of Vecchio weeping over the body of one of four students shot dead by the Ohio National Guard became the symbol of the Kent State Massacre and of the agony of a nation torn apart by the Vietnam conflict.

Florida officials quickly branded her a communist dissident even though her identity was unknown.

With her picture transmitted around the world, Vecchio tried to slip away and catch a bus to California. Police tracked her down before she could board and sent her home to her family. She eventually married and moved to Nevada. Although she never attended Kent State, she was invited to the campus several times for memorial services.