At the end of the Monty Python film Life of Brian, a happy character who has been sentenced to death by crucifixion cheerfully sings and whistles, "Always look at the bright side of life!" Soon a long row of other crucifixion victims begins to sing along. This scene comes to mind after viewing Polish conceptual artist Zbigniew Libera's traveling exhibition "Positives," which similarly combines the infectious power of positive thinking with strong doses of irony and social commentary.

"Positives" was first shown in September 2004 in Poland. Nine photographs from this much larger project have traveled extensively since then, especially in the United States. They are all based on iconic images of tragic or stark historical events captured by photojournalists over the past century. Libera re-enacts the staging of these photographs, but he creates a positive story line.

The infamous Vietnam War image that showed napalm-soaked children fleeing the village of Trang Bang in agony following a U.S. military bombing is restaged and titled Nepal. It now shows a group of smiling children and a laughing naked woman with arms outstretched running down a desolate road or airfield runway, with a group of recreational skydivers behind them instead of the military personnel in the original photo.

A famous photograph from the end of World War II that recorded grim-looking Auschwitz prisoners at the moment of liberation is recast with a group of smiling men and boys wearing striped pajamas or winter coats or wrapped in blankets, standing behind a fence made of string (instead of barbed wire). It is titled Residents.

By re-imaging these iconic photographs, Libera successfully forces viewers to reassess the automatic emotions, such as revulsion or horror, that are triggered when we view tragic (but also ideologically loaded) images.

For instance, Cyclists shows a group of bike riders in helmets and colorful spandex outfits pulling down a stop sign at a border crossing. According to an assistant at the Polish Institute, this was one of the most successful images from the "Positives" series in Poland, because it re-enacts a well-known photo of German soldiers taking down a border post near Gdansk in 1939.

Another photo comes from the contemporary Polish media, but the image speaks to all of us in an instant. It is a blown-up reproduction of the cover of a popular Polish magazine showing a young Muslim woman hugging a U.S. soldier, apparently in gratitude for toppling Saddam Hussein's regime. The photo was taken April 13, 2003, two days after the U.S. military entered Baghdad, and it was re-used in a billboard advertising campaign for the magazine all over the country — at the same time serving as propaganda to build Polish support for the coalition forces in Iraq.

Though all the works in Libera's series are based on actual photographs, some images could be set almost anywhere, especially Massacre at a Cross-Country Race. It shows bodies sprawled out on a beach or vast sandy plain, at first glance looking like a mass of corpses surrounded by grieving villagers. On closer examination, the bodies aren't massacre victims at all, just exhausted runners. Our quick perception of the race onlookers as mourners is a keen visual and conceptual trick by Libera.

Just as effective is the photo titled Workers, which invokes an iconic pose of guerilla rebels in Central America. Three young men stand in a jungle wearing red bandanas and partially shielding their faces, but instead of holding machine guns, one holds an electric sander and another an electric drill. The third stands behind them, wearing a construction helmet and a loaded tool belt. For people worried about immigrants usurping more and more manual jobs in their homeland, this image could still trigger fear.

Libera (born in 1959) splits his time between Warsaw and New York City and is one of the most provocative artists at work today. Under martial law in 1982, near the beginning of his artistic activity, he was imprisoned for making and distributing anti-government flyers and pamphlets. However, he expects no sympathy for this experience. When asked in an interview whether certain works reflect his prison experience, he replied matter-of-factly: "I am neither the first nor the last artist who landed in jail."