If you are one of those fortunate souls who, in an age of needless bloodshed, environmental catastrophe and economic meltdown, stubbornly persists in believing the world is a generally swell place, this is the book for you.

Its 'creator' and editor David Elliot Cohen is best known as the co-founder of the immensely popular Day in the Life series, which sought to shed light on the soul of his native America and other countries through a marriage of striking photography and prose. Here, Cohen has kicked the concept up a notch, inviting dozens of heavy-hitting photojournalists, expert commentators and other writers to contribute chapters on the issues that trouble them most, resulting in a kind of enormous grab-bag of human depravation and social ills.

The aim, Cohen admits frankly in the introduction, is not just to make the reader think, but to 'react with outrage ... and create an uproar'.

That What Matters is a different animal to most photo-essay volumes is apparent from the first few pages, which begin with some historic - and morbid - images of child factory workers and war dead. The unusual nature of the book raises questions: should it be judged as a work of photography, literature, activism or all three? If a picture is worth a thousand words, what are a picture AND a thousand words worth? And finally, are there any good reasons for readers to subject themselves to more than 300 pages of all that has gone wrong with civilisation, in vivid, despair-inducing colour? Whatever the answers, these essays depict a reality that must be seen and has too often remained on the periphery of the media's vision.

Many of these images will burn themselves into the reader's consciousness, either because of the immediate tragedy of the subjects - a chemical-blackened three-year-old sitting on a window ledge in a factory in which she works in Bangladesh, for example - or the unspeakable horror that they suggest, as in the picture of an evacuated kindergarten near Chernobyl filled with ghostly, abandoned dolls.

Others, however, fall flat, like the surprisingly standard-looking urban panoramas from Gary Braasch that are supposed to depict the evils of climate change. One could also take issue with the chosen subjects: why is the US-Mexican border more deserving of coverage than the hundreds of other crossings that see far more refugee traffic and deaths?

The words fare less well than the pictures, almost always ignoring the images they frame and couching crises in general terms, relying heavily on statistics and rather trite calls to arms. Economist and philanthropist Jeffrey Sachs suggests 'strengthening the UN' and adopting a 'plan of action' would help reduce global poverty. Does he really think no one has tried?

There are exceptions, such as Salon writer-at-large Gary Kamiya's masterful slice of prose on media coverage and images of Iraq's American war dead. But in the end it is largely left to the pictures to tell the tales - a job they do admirably.