Photojournalism is a strange way to make a living. For one thing the living you make is pretty marginal; it's not a career anyone ever undertook for the money. Furthermore, the working conditions under which you earn the pittance offered are appalling. They include getting shot at, being sleep and food deprived, spending way too much time in the coach section of an airplane, and way too little time at home. There's a reason that photojournalists don't have a union – any union organizer worth his or her salt wouldn't know where to begin righting the wrongs. And yet paradoxically it's also a life of incredible privilege. The average photojournalist, if there is such an animal, gets to go to more places, meet more people and experience more things than one could reasonably expect to force into three or four ordinary lifetimes. What other career would give its practitioners the opportunity to witness the fall of Saigon, photograph Louis Armstrong, Andy Warhol and the cast of "Star Trek," document eight presidencies, including accompanying Nixon on his historic trip to China, and to capture Clinton hugging an unknown White House intern named Lewinsky? This job gives those who embrace it an unparalleled front seat in the long-running show called history. The reason that most photojournalists put up with the low pay and difficult circumstances is that they are amazed they are allowed to do what they do.

The word "allow" in this context is a modified use of the verb. This is not a career for the fainthearted; wallflowers need not apply. It takes an immense amount of determination and a certain level of pushiness to achieve any level of success. The barriers encountered on a daily basis include presidential advance people, military information officers, the public relations employees of major (and minor) celebrities, and security guards of all descriptions. On top of all this it is often necessary to intrude into the most intimate moments of people in abject circumstances in order to bring a story to the wider world. Few photographers like to photograph the dying, the grieving or the victimized, but often the job demands it, and it is these photographs that on occasion actually do make a difference. For an intelligent and responsible photojournalist the moral and ethical minefields can be almost as unnerving as the real thing.

Those who make a living telling the stories of our time with their cameras are equally adept as raconteurs. Some of the most enjoyable moments of my career have been spent in the company of photographers sitting around telling 'war stories' – often, of course, stories about actual wars, but equally compelling are the tales about other battles fought, mostly with various authorities, and especially their own editors. The reason that photographers' stories are so absorbing is because they tend to focus on the emotional aspects of any experience. Emotion is the lingua franca of photography, and the reason for its long-lasting appeal. It is not a medium that is good at analyzing why something happened, but it is unequalled in telling you what it felt like when it happened. So too are the stories that photographers tell about the work that they do. If you don't believe me now, you will by the time you've finished reading this book.

Dirck Halstead has been a photojournalist for 50 years, starting out as a precocious high school student snapping a picture of Rita Hayworth leaving a courthouse in White Plains, N.Y., in 1954, and now engaged as an equally precocious Senior Fellow in Photojournalism at the Center for American History at the University of Texas, Austin. In between these points he has been a UPI picture bureau chief and photographer in Saigon, photographer for both Life and Look magazines, but most of his career was devoted to Time magazine in Washington, rising to the position of Chief White House Photographer. He was one of those members of the White House Press Corps that presidents knew by their first names.

Dirck's career has also spanned an era that will be regarded as pivotal in the history of photojournalism. It has been a period during which the profession has had to constantly reinvent itself as it responds to the new demands and opportunities, or sometimes lack thereof, of technology and market changes. It used to be that news stories were shot in black and white and transmitted over the wire by AP and UPI, whereas magazine stories were mostly shot in color and often carried back from foreign locations by unsuspecting airline passengers. Can you imagine going up to a complete stranger at an airport today and asking them to carry a package of what you swore was film that would be collected by somebody you swore was a representative of the magazine upon landing? In the early Seventies this was about the only way to get color film back to the picture desk, and the flying public was more than happy to oblige. They seemed to like this albeit tangential connection to the glamour of international journalism, although their enthusiasm might have been muted had they known that they were called 'pigeons' by the photographers they were helping. Today film is virtually irrelevant in documentary photography, and with PowerBooks and satellite phones photographers can, and do, transmit digital files directly to their newsrooms from the middle of a firefight in Iraq.

The market for this kind of work has changed dramatically as well. Of the three magazines that Dirck worked for as a photographer, Time is rapidly losing readership, Life is a sad newspaper insert of its former self, and Look hasn't been around as a weekly magazine since 1971. Television, which was prematurely credited with the death of photojournalism, is itself now under threat as a news source from the immediacy of the Internet, which represents significant possibilities as an outlet for journalistic photography. In fact, Dirck is one of the people creating these opportunities with his Webzine The Digital Journalist. The first law of survival is the ability to adapt to new circumstances.

What is the merit in a life spent chasing images to illustrate magazines? For a democratic society the value is great. There's a good reason the Founding Fathers of this nation made the First Amendment the first amendment, and not the fourth or fifth. They understood that for a democracy to function properly the people would need both information and transparency in government. Photojournalists are among the people who provide both, and in the form that we trust the most, even in these days of digital manipulation. Seeing it with your own eyes has long been the standard for believing that something is true, but we do not get to witness most of the events in the world that are important to us; we have to see them through other people's eyes, people like Dirck Halstead. He and his peers are our eyes and ears on the frontline of current affairs, and although we don't always believe what reporters write about a presidential candidate, or a flood, fire or earthquake, for the most part we do believe what photographers shoot. For one thing they have to be there; you can report a war from a hotel lobby, but you can't shoot one from the same location.

By any yardstick Dirck's career has been remarkable in both its length and breadth. He has witnessed many of the key events of the last half of the 20th century, some of whose importance was obvious as they happened, and others that have increased in significance as time went by. Not the least of the latter group is the photograph of President Clinton embracing an obviously adoring intern called Monica Lewinsky. Photographers have prodigious visual memory; they sometimes can't remember if they've done their expenses but they can tell you exactly what they shot 20 years ago and on what lens. After the Lewinsky story broke Dirck remembered that he had seen her face somewhere before and after considerable research discovered that he had already shot her. Unfortunately for President Clinton it has become the iconic image of his presidency. But that's what history is essentially – a constant reevaluation of events.

This book is not just a collection of one photographer's photographs; these moments in time are our history brought to life. Although Dirck owns the photographs, through them we own the moments. If the most important light reading for a photojournalist is f/8 and be there, then Dirck Halstead got his exposure right every time. Not only are we better off for him being there, but it is also his legacy for generations to come.