There is a passage in Despatches, Michael Herr's viscerally powerful memoir of his time as a war correspondent in Vietnam in the late 60s, in which he describes seeing a photograph of an American marine "pissing into the locked-open mouth of a decomposing North Vietnamese soldier".

He goes on to describe albums full of what soldiers call trophy photographs, some with pictures of Viet Cong women who had been stripped and humiliated, others with more graphic images of grinning American soldiers holding up the severed heads of Viet Cong fighters or necklaces made of human ears.

"There were hundreds of those albums in Vietnam, thousands … " Herr wrote. Most of them were never at the time seen, except by the soldiers who took them and the soldiers that posed for them. In 1970, though, the court martial of 14 American army officers for their part in the infamous My Lai massacre of 16 March 1968, in which over 400 civilians were killed, relied heavily on photographs taken by an army photographer, Ron Haeberle. He had taken them on his personal camera and kept them hidden until November 1969, when he sold them to CBS news.

In her thought-provoking new book, Private Pictures, Janina Struk mentions the My Lai photographs only in passing, and with particular reference to the more recent images of American soldiers abusing and humiliating Iraqi prisoners in Abu Ghraib prison. "Like the Abu Ghraib pictures," she writes, "those taken at My Lai had come to symbolise all that was wrong with the war in Vietnam – although they never became iconic images."

The world has changed since then. Now anyone with an internet connection can see countless images of war atrocities, gruesomely posed trophy shots and even footage of casual but deadly violence against civilians, all taken – and often disseminated – by serving soldiers. In a chapter called "The Inside View of War", Struk concentrates mainly on one website which, by 2005, "had more than 150,000 registered users, including about 45,000 military personnel and 180,000 daily visitors accessing amateur pornography and more than 5,000 (mainly American) soldiers' pictures".

The book traces the history of soldiers' photographs, which are almost as old as photography itself, beginning with a small stash of black-and-white portraits discovered by the British war reporter Robert Fisk in 1998 in the attic of his mother's house. They were taken by his father, Second Lieutenant William Fisk, who had served in the first world war. They seem innocent now – posing comrades, a few single portraits, a murky view of no man's land taken from a trench in France in the last days of the war – but they were illegal, and possession of such private pictures could lead to a court martial and a possible death sentence. Despite this, as Struk notes, "thousands of soldiers from all sides took their cameras to the first world war. The question was, why?"

It is a question that resounds though this fascinating book, and the answer seems to have more to do with human curiosity and the urge to record one's personal experience to compare it with – or set it against – the official view of history. One dramatic recent example of this was a photo exhibition entitled Bringing Hebron to Tel Aviv, curated by Breaking the Silence, an organisation made up of former soldiers who had served with the Israel Defence Forces in the occupied Palestinian territories. By revealing their private pictures and thus breaking the law, they were, writes Struk, "confronting Israel society with the photographic evidence of what they called the 'terrible moral price' of occupation and asking it to judge for itself".

In a strangely mundane way, Stuart Griffiths's new photobook, sarcastically titled The Myth of the Airborne Warrior, asks the same kind of question – albeit rather belatedly – of British society. It is made up of Griffiths's personal snapshots of his tours of duty in Northern Ireland as a young soldier with the Parachute Regiment. The photographs, which were taken on a humble Canon Sure Shot, often look snatched or have been taken from a distance so that the housing estates and streets of tribally divided, working-class Belfast look even bleaker and more threatening than they are. He captures his fellow paras at rest and at play – one guy poses with a rifle barrel in his mouth; another shows off his black eye – as well as on patrol though the republican areas, where the graffiti singles out the paras for particular loathing and disdain: the fallout from their killing of 13 civilians on Bloody Sunday in Derry in 1972.

The small book has little context save for Griffiths's own first-person text, which has been heavily edited in black marker to highlight the most shocking anecdotes in direct contrast with the mundanity of the images. There is also a short essay by Gordon MacDonald of Photoworks that concentrates on the images as evidence of Griffiths's personal experience as a serving soldier from a working-class background, which began with "great aspiration" and ended in "severe disillusionment".

Tucked into each copy of this first print run of 500 are ephemera from his time as a squaddie: anti-British army leaflets distributed by the IRA; an official government leaflet outlining "instructions for opening fire in Northern Ireland". I also received a signed print of one of the photos: a pretty amateurish portrait of a soldier standing in front of a republican paramilitary mural – taken from a safe distance. It made me feel oddly nostalgic for my misspent youth being daily harassed by working-class guys in uniform like Griffiths and the dangerous thrill of taking revenge with bricks, bottles and some obscenely poetic taunts about their parentage and their homeland. An odd little book, then, of one soldier's wilfully unprofessional but curiously revealing photographs – but an evocative one for that very reason.

Now see this:

Believing Is Seeing is an intriguing group show at Ffotogallery, Cardiff, comprising the work of seven contemporary artists from Korea who utilise photography in different ways. The unifying theme is Korean-ness, as implied in the "Junsinsajo" portrait painting tradition, which replicates the subject's shape and spirit. From 10 November to 17 December 2011.