This photograph was taken at the picket line at the Ford Dagenham strike of 1968. Female machinists had walked out in protest at being paid less than their male counterparts for equivalent skilled work. Moon had just arrived at the site when the postman came to deliver the mail; in this photograph, she captures the moment when he decides not to cross the picket line and turns back, cheered by the striking machinists. Notice how the focus of the photograph is not the postal worker himself, who is caught leaving the shot, only his shoulder and bag visible. Rather, Moon draws the watcher’s eye to the three women in the foreground of the photograph, the interplay between their bodies, arms linked, and the tilt of their heads as they laugh. The image is reminiscent of Land Girl publicity posters and seaside holiday snaps, and connects to our ideas of women as sisters, united and formidable.

The women here are strong, good-humoured and full of purpose; the camera’s view is steady and honest. Behind the trio of faces the photograph focuses on, you’ll see another group of women; the one on the far right is the second wave feminist and writer Leonie Barratt, a long-term associate and close personal friend of Moon.

This early photograph bears many of the trademarks of Moon’s later work. The focus is sharp: as with her later portraits, there is no desire to hide flaws or soften images. The photographer draws our attention to the faces of her subjects by positioning them a third of the way down the frame. And there is nothing static or posed about this photograph. It is a moment captured that would otherwise have been lost.

This is the first of Moon’s images to have been published in the UK national press, when it appeared to accompany a column by Leonie Barratt in This Month magazine, in July 1968. This Month was published from 1962 to 1986 and published a range of reviews, features and columns, with a readership of 250,000 at its peak. It could be seen as the first photograph of Moon’s feminist career. Many of the photographs that Moon took previously while working at the Colchester Echo do feature women, but these are in traditional roles – at coffee mornings and charity events. Moon was assigned these jobs while her male colleagues were given news and sports stories to cover; she went to Dagenham on her day off, having been refused permission to attend as an official photograph by the Echo’s editor.

In 1968:

• Harold Wilson was Prime Minister of Great Britain

• In the USA, Senator Robert (Bobby) F Kennedy and Martin Luther King were assassinated within three weeks of each other

• The Beatles had two number one chart singles in the UK with ‘Lady Madonna’ and ‘Hey Jude’

• Enoch Powell made his notorious ‘Rivers of Blood’ speech

• The TV show Dad’s Army was first screened