WHEN Edward S Curtis decided to embark upon a photoethnographic study of the North American Indians in 1906, he was one of America's most highly regarded photographers. He had risen from a childhood of poverty to run a successful photography studio in Seattle, and had even come to the attention of president Theodore Roosevelt.

But what was initially conceived as a five-year project ended up becoming an epic, 30year undertaking, unprecedented in its scale and scope and leading to unforeseen personal sacrifices. It ruined his emotional and physical health, led to his divorce and separation from his children, and resulted in the loss of his studio. The man who became known as Shadowcatcher to the Native Americans died in obscurity in 1952, destitute and forgotten.

But Curtis left behind an astonishing legacy, which has attracted increasing attention in recent decades. The North American Indian consists of a 20volume set of handmade books, with more than 2,000 original photographs of some 80 tribes and almost 4,000 pages of text.

In total, he made nearly 50,000 negatives and 10,000 recordings of languages and music.

The project, which was partly sponsored by JP Morgan, would have cost a staggering $35m in today's terms. It's no surprise, then, that it has been hailed as one of the largest photoethnographic studies completed by a single man, with the New York Herald describing it as "the most gigantic undertaking since the making of the King James edition of the Bible".

An exhibition at the Gallery of Photography in Dublin features a tiny fraction of the photographs from The North American Indian.

Entitled Sacred Legacy, it is an astute selection of images which demonstrate the breadth and range of Curtis's work.

It also reveals the degree to which his photographs have come to epitomise popular perceptions of Native Americans. Chiefs decked out in jewellery, costumes and regalia have characteristically proud, stoic expressions. In many photographs, the Native Americans are engaged in traditional, everyday activities, such as a man poised to spear a fish or a woman weaving a blanket.

They are shown to be at one with nature, as in 'At the Pool (Apache)', in which an almost naked man stands at the edge of an expanse of water, contemplating the peaceful scene.

The aesthetic, pictorial quality of Curtis's work is unsurpassed, from the grandeur of the Great Plains landscapes to intimate portraits of individual figures. There is a classical balance to his images, with a masterful use of light and shade and a notable attention to detail.

The quality is also of the highest order: the majority are photogravure prints, one of the most expensive, difficult and effective methods of production at the time.

It is strange, however, that the exhibition does not allude to the more controversial aspects of Curtis's oeuvre. As an ethnographic project, The North American Indian continues to spark debate among scholars and Native Americans. Curtis has been accused of romanticising Native Americans, of idealising their way of life and of exoticising them as the 'other' - the noble savage.

It has often been noted that he actually paid his subjects to dress up in traditional costumes and reconstruct rituals and events. Curtis's photographs are in many ways a fiction - a recreation of a past already lost.

These photographs were taken at a time when the US federal policy of forced assimilation was in full swing, demanding that Native Americans forsake their way of life and integrate with the dominant culture. Some critics, consequently, have argued that Curtis would have better served their cause had he photographed the communities, not as an idealised representation of the past, but in their true state of affairs:

starving, poverty-stricken and subjugated.

But for many, his images continue to offer a glimpse into a past which would otherwise have been lost. As he said: "The information that is to be gathered, for the benefit of future generations. . . must be collected at once or the opportunity will be lost for all time."

It is a pity that the exhibition does not engage with these complexities, which make the legacy of Curtis's endeavours all the more worthy of study and debate.

"It's such a big dream, I can't see it all, " was how the Shadowcatcher once described his project. The same could be said of this fascinating but patchy exhibition, which only presents one side of the story.

'Sacred Legacy' continues at the Gallery of Photography until 21 January