In 1936 the photographer Dorothy Lange captured an image of a young mother that came to be one the defining images of the Great Depression, a worldwide economic catastrophe that followed on from Black Tuesday – aka the Wall Street Crash of 1929. It would last until the late 1930s, which is to say, ironically, sadly and paradoxically, it came to an end with the beginning of World War II.

It is both a portrait of a woman and a mother, simultaneously a picture of an individual and a family all at once. It is unique. Due to the picture's natural composition, the perfect moment of capturing history between the compress of a finger upon a shutter and the soft recoil as the button returns to its natural static shape, it is a sweeping indictment of everything that was wrong about society during the interwar periods.

The black and white picture is of a forlorn looking woman called Florence Owens Thompson, the fingers of her right hand resting to the side of her cheek, anxious, awkward, tired and hungry, her eyes suggesting a feeling of being utterly at a loss. Her two young children are nestled on either side of her, facing away, resting upon their mother, basking in her comfort regardless of their deprivations.

She looks a lot older than her 32 years, which comes across as tragic, unfair even, aged by the brutality of her existence. Her solitude – too hungry and tired to be lonely per se – is palpable too. Her husband had died of tuberculosis.

The family survived on a meagre diet – her kids hunted birds and where possible, they sourced whatever vegetables they could at the migratory labour farm in Nipoma, California. It was a case of one day at a time – in America, which had been known for the lavishness of the Roaring Twenties.

Reflecting on the picture in the 60s, Ms Lange said: "I saw and approached the hungry and desperate mother, as if drawn by a magnet. I do not remember how I explained my presence or my camera to her, but I do remember she asked me no questions. I made five exposures, working closer and closer from the same direction. I did not ask her name or her history.

"She told me her age, that she was thirty-two. She said that they had been living on frozen vegetables from the surrounding fields, and birds that the children killed. She had just sold the tires from her car to buy food. There she sat in that lean-to tent with her children huddled around her, and seemed to know that my pictures might help her, and so she helped me. There was a sort of equality about it."

For aspiring photojournalists, this is a perfect image to study in terms of holding true to the adage that a picture can tell a thousand words. Simple, true and unapologetic, the story of one woman was quickly reproduced in newspapers across the world. Everyone felt her pain – they were going through it.