Lucie Myslikova, a member of the Czech Scout group Junak, was photographed by amateur photographer Vladimir Cicmanec at a protest in Brno, the second largest city in the country.
Posted on the Facebook page of the World Organisation of the Scout Movement, the image features Myslikova standing calmly, juxtaposed against a demonstrator wearing all black with sunglasses and a shaved head.
"She was standing tall and she's 16 years old and she stood proud and made some profound arguments," Cicmanec told CNN.
"I didn't hear all of their exchange but they were talking about the concept of nations and nation-states, immigration, refugees," he said.
"She tried to explain to him that nationalism makes no sense because we are all people and should not be treated differently based on some arbitrary distinctions."
Shared with the image was a message from the scout organisation promoting a message of inclusiveness and understanding.
"People from all walks of life, and #Scouts among them, came to the streets during an extreme right march yesterday, to express their support for values of diversity, peace and understanding. Creating a better world"
The scouts were counter-demonstrating against a May Day rally held by ‘neo-Nazis’ who were marching in support of leaving the European Union, outnumbering the ultra-right advocates two-to-one.
In Sweden a similar image was shared at a demonstration in Borlange, with activist Tess Asplund raising a defiant fist in resistance to the Nordic Resistance Movement.
The photo was taken by Stockhom-based photographer David Lagerlof.