(CNN) — The images look decades ahead of their time: color stills of 19th century scenes, sharp and beautifully rendered in earthy shades evoking the dry heat of their setting, North Africa. Not paintings, but not photographs like you and I know them today. Something in between and a treat for the eyes.

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Men huddle around a snake charmer while women congregate in the shade nearby. Across sprawling cities minarets push up into the sky, alongside colonial ports replete with rococo arches and neo-classical columns. Muslims in traditional robes and Christians in European livery walk streets apart, but never appear to meet. They represent a tale of two cities, colonizer's and subject's, depicted in carefully constructed peace.

These extraordinary images, living deep within the archives of the Library of Congress, capture a fleeting moment in history on the cusp of the 20th century. Dated from approximately 1899, their authors are largely unknown, while the technique behind them has long gone out of practice.

Called photochroms, a form of photolithography, these high end portraits of life in colonial North Africa are a time travel tour through a forgotten era; rich with politicking and not always the innocent postcards they may seem. So what secrets and hidden insights do they contain?

The origins of the photochrom

The 19th century marked a period of unparalleled growth in industry, engineering and empire. The world had opened up: travel became easier as liners crossed oceans in record speeds and the proliferation of railway lines prompted Great Britain, the home of GMT, to rethink time itself

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For the privileged few, horizons were expanded. A colonial class settled into enclaves from Agra to Algiers, while European tourists wishing to venture beyond the continent had never had it so easy. Exoticism was sought and found, with other cultures recorded and represented -- though not necessarily understood.

By the end of the century Europeans were setting up cameras all across North Africa, capturing scenes from an array of colonial cities. Egypt was a British protectorate, Algeria a French colony; Tunisia a French protectorate while Morocco, not yet a Spanish and French protectorate, nonetheless had a heavy European presence. Libya, meanwhile, was not yet unified and part of the Ottoman Empire.

The photochrom, developed in Switzerland, 1890 after 10 years of research, was a breakthrough in photography, says Helena Zinkham, chief of the prints and photographs division at the Library of Congress.

"A lot of people think all old photos were black and white and brown," she says, "but in fact the drive to introduce color into photography was almost from the start the invention."

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To make a photochrom "you take the negative from the camera and expose it on to stone or zinc -- a very flat surface," Zinkham explains.

Before exposing, a coating of light-sensitive chemicals is applied to the flat plate, which hardens in accordance with the light filtered through the negative, creating a print. Different exposure durations would transfer different shades of the monochrome negative, meaning up to 24 separate plates could be made, each representing a different color.

The photographer would create extensive notes so the photochrom printer could then ascribe different colors to different plates. Printed on top of another, ink would bleed and create shading and photorealistic results.

"By switching out to the lithography process you could print hundreds of thousands of copies," Zinkham says. High quality and cost effective, these professional images soon circulated around the world, with companies in London and the US licensing the patented process.

Antique art or propaganda pieces?

Charlotte Chopin, lecturer in French studies at the University of London Institute in Paris, describes the prints as "part of the European capitalist economy of mass cultural production that is geared towards European clientele." Indeed, while many of the images portray indigenous people, Chopin, a specialist in colonial Algeria, says she's seen no evidence that photochroms were circulated among indigenous communities.

The photochrom became a shop window for the European traveler: a sailing trip down the Nile, a visit to the souks, while selling the achievements of the colonial model.

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"[They] contrast the European imprint of the city with the indigenous people... something that would probably appeal to tourists, to see the contrast with European architecture and the streets where the indigenous people were living," says Arden Alexander, cataloger specialist at the Library of Congress.

Indigenous people became an attraction in and of themselves -- but also served a political purpose.

"I think some of [the photochroms] look very much Orientalist," argues Chopin. "Orientalism was absolutely crucial to power structures of colonial rule, because it was about stereotypes that portrayed North African peoples in a particular way, either as indolent, mysterious or dangerous -- or irrational." These stereotypes could then be used to legitimize colonial domination, the lecturer says.

"Moorish women" and an "Arab juggler" are pictured and annotated by photographers, but denied a voice. The colonial eye keeps "control of the frame," argues Chopin, saying the photochroms omit evidence of the many forms of violence exacted by colonial powers on indigenous populations to maintain authority.

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"The images are really romanticized... it looks peaceful," she says, "people looking happy and tranquil. I don't think that's at all accurate for anyone really living in North Africa."

But Chopin also argues that there could be a subversive element to their exotic, Orientalized images.

"One of the things other scholars talk about is performance: performing the perceptions that Europeans have of Algerians and Tunisians in order to, behind the scenes, carry on and protect your own culture... because on the surface you're performing the culture you want to see," she says.

End of an era

The First World War brought a curtain down on this era of photography. By the time peace treaties were signed camera technology had moved on, and tourists were more likely to take their own pictures, rather than purchase a photochrom. The cultural landscape in North Africa had changed too, as populations found their voices and sought reforms from their colonial masters.

These images, nostalgic but containing a rich, and sometimes dark subtext, were now objects of a past epoch.

Today photochroms are collector's items, and held in museums and libraries. But with the digitization of archives, some collections are finding a new lease of life online.