"To photograph people is to violate them," wrote Susan Sontag in her seminal work, "On Photography."

"By seeing them as they never see themselves, by having knowledge of them that they can never have; it turns people into objects that can be symbolically possessed."

Revolutionary in its unflinching critique of an art form that was just taking shape, the book first published in 1977 has gone on to become something of a bible for art theorists interested in tracing photography's role in society. Its language has been adopted, Sontag's criticisms accepted or rejected at hand.

But do Sontag's criticisms of the portrait still hold true today? Are people, when photographed, turned into a commodity?

In the nearly 40 years that have passed since "On Photography" debuted, portraits have become ubiquitous. Possessing an image of one's own likeness is far removed from the days of John Singer Sargent's oil paintings - no longer a luxury afforded only by the wealthy elite. Indeed, Sontag's critiques appear to have borne fruit.

"Needing to have reality confirmed and experience enhanced by photographs is an aesthetic consumerism to which everyone is now addicted. Industrial societies turn their citizens into image-junkies," she wrote.

In a world where "selfies are becoming a sport," as writer Rachel Syme tells us in her lengthy homage to the new art form, what, if any, relevance does the photographer's portrait hold?

Artists under the influence of their subjects

"With Different Eyes. The Portrait in Contemporary Photography," comprises two simultaneous exhibitions that explore that question. A timeless subject, the portrait maintains its relevance across the spectrum of art history; this exhibition takes up the question of how it has been re-innovated to fit into today's highly-commodified, image-saturated world.

It's a unique exhibition that takes up two spaces both literally and metaphorically. One part of the show opens February 25 at the Kunstmuseum Bonn and runs through May 8. In Cologne, Die Photographische Sammlung/SK Stiftung Kultur will hang additional works in a show running from February 26 to May 29.

Each museum draws on its own strengths to consider a unique angle as it explores the subject. At the Kunstmuseum, the artists' range of approaches span from documentary to mise-en-scène, from restatements of iconographic picture traditions to the artistic occupation with amateur photography. In Cologne, where the field of documentary photography is strengthened by the August Sander Archive, the exhibition's focus lies on serial portraits that follow an artistic-documentary approach. The result combines portraits from the institution's private collection side-by-side with works extracted from nine photographers from around the world.

It's a particularly comprehensive overview of portrait photography in the 21st century and showcases powerful works by dozens of artists. Given great freedom, the artists make use of their medium to create their own worlds - single photographs appear alongside photo sequences and room-filling installations and cinematic works. Whatever the form, the artists appear to be most influenced by their subjects.

The men of the Arctic

Works by Mette Tronvoll, which were taken as part of her 20-part series documenting her native Norway's arctic island archipelago of Svalbard, with its stunning natural landscapes and an otherworldly atmosphere created by the climate there, are included.

With its only residents now comprised of biologists and meteorologists, researchers who have arrived to do important work on the impact of climate change, Svalbard has changed since its previous days as a mining community. It's that shift that Tronvoll captures in her portraits of the men in their new arctic home.

Also on display are portraits taken by British photographer Mark Neville, a war artist who embedded with British troops in Afghanistan for four months from 2010 to 2011. Excerpted here from his book, "Battle against Stigma," the pictures were Neville's attempt at building bridges between the soldiers he accompanied with the people in the country.

"You can see in their eyes, that their contact with me and with the camera was influenced by the fact that I was surrounded by men with machine guns. That we were in a war zone," according to Neville.

Taken individually, the portraits capture a particular time and place in our modern world. They are, as Sontag would say, a contemporary way of "imprisoning reality." Taken all together, however, the portraits are something different. Not the narcissistic commodity that a selfie represents nor a violation as Sontag may have put it, but a mere capturing of the soul in a particular moment.

The images represent a powerful juxtaposition of our diverse and divergent realities today, as seen in the eyes of strangers. With different eyes, if you will.