Some five metres from the Scottish National Portrait Gallery entrance currently resides arguably one of the most powerful images to ever grace the building, one publicizing Scottish photographer Graham MacIndoe’s harrowing yet breathtakingly candid Coming Clean.

This grainy photograph, captured on a cheap digital camera, has a languid Macindoe awkwardly sprawled across a wooden bench, his face pinched, contorting from the overwhelming immediacy of intravenous injection. Blood ribbons across the forearm propping up his heavy head, having just received a rather different substance than the tattoo ink sitting below the surface of his skin.

The image turns the heads of almost all the Gallery passers-by and little wonder why; it’s a picture painful to absorb, triggering that innate horror of viewing another human in such an incapacitated, helpless condition.

In the minutes prior to it being taken eight years ago, Graham MacIndoe rolled up the sleeves of his ragged red sweatshirt and began cooking up heroin in a dilapidated drug-den in a Brooklyn Projects tower block. Bottles, needles and litter surrounded him, the debris of addicts who’d freely come and go. Taped to walls were tattered duvet covers, as makeshift insulators. Morning's light, piercing through bed sheets in place of curtains, soared in.

Across the New York skyline lay the iconic neoclassical copper statue of the Roman Goddess Libertas, Manhattan's eminent maritime monument now famously symbolic of the freedoms America offers those who enter her. One of the arms on the Statue of Liberty imperiously raises a flaming torch in the celebration of liberty. At her feet, the shackles of enslavement.

Back over the Brooklyn Bridge, however, the settler MacIndoe was anything but free, rather trapped in a torrid trench of debt, self-destructiveness and devastating daily cocktails of heroin and crack cocaine.

The burgeoning Big Apple career of a boisterous Broxburn boy had all but collapsed. Long gone were the photo-shoots, his house and – estranged from his son, family and ex-partner – effectively everyone in his life. Jail time in the notorious Riker’s Island prison and an American immigration centre awaited him, the nadir of a decade vanquished to substances. This image would come to encapsulate the whole downward trajectory, and for MacIndoe, the end of the road.

The photographs are the result of a powerful interdependence between MacIndoe’s strong compulsions, the drive to capture his addiction’s consequences, and of his dexterous ability to do so. Everything was gone, the career, self-discipline, his mental health, yet here he was reaching out for the only thing that remained, the sole facet he’d been left with any discernible control over; his camera. Little could he have known that the picture would one day adorn his native national art institution as the flagship photograph for one of the most challenging photography exhibitions ever mounted.

Nor could he have anticipated that his compulsion to turn the camera around and document his descent would be catalytic for countless others to escape their own – Coming Clean has produced an unparalleled response from the public. The exhibition’s comments books are laden with heartfelt responses from addicts and those impacted by addiction, messages mirrored in the myriad expressive comments made to Gallery staff. The public have gone through boxes upon boxes of informative addiction leaflets accompanying the show, from organisations such as CREW. MacIndoe himself has had moved members of the public to stop him in the space, searching for ways to tackle their own issues.

This extraordinary response was also patent in the packed artist’s talk he recently gave at the Scottish National Portrait Gallery, where the audience heard about the punk turned painter who pursued photography after encouragement from his Edinburgh College of Art tutor, the late Murray Johnston.

Eight years ago, MacIndoe was slipping in and out of unconsciousness, trapped by addiction. At the talk, he slips in and out of subjects with humour and grace and, with an hour to unpack a tale that could take a year to tell, is trapped only by the limitations of time.

Here he delves into dependence, its difficulties and the ongoing vigilance required, but focuses equally on the joys of recovery; of living healthy, of closing the distance with loved ones and friends; of reconnecting with ex-partner Susan Stellin, with whom he's now happily married; of co-authoring a book with Susan and of flourishing again in his career as a photography professor at New York’s prestigious Parsons The New School (where, he says, he’s “part professor, part social worker”).

His is a simply staggering recovery, from heroin addict to a happy, vibrant, picture of health, a transformation beautifully encapsulated by The Scotsman’s Susan Mansfield, with, “He is aware that, powerful as the photographs are, the most important exhibit is, in a sense, himself: after the destructiveness of addiction portrayed in the pictures, he is living proof that recovery is possible”.