Callahan left almost no written records—no diaries, letters, scrapbooks or teaching notes. His technical photographic method was to go out almost every morning, walk through the city he lived in and take numerous pictures. He then spent almost every afternoon making proof prints of that day's best negatives. Yet, for all his photographic activity, Callahan, at his own estimation, produced no more than half a dozen final images a year.
He photographed his wife and daughter and the streets, scenes and buildings of cities where he lived, showing a strong sense of line and form, and light and darkness. Even prior to birth, his daughter showed up in photographs of Eleanor's pregnancy. From 1948 to 1953 Eleanor, and sometimes Barbara, were shown out in the landscape as a tiny counterpoint to large expanses of park, skyline or water.
He also worked with multiple exposures. Callahan's work was a deeply personal response to his own life. He encouraged his students to turn their cameras on their own lives, leading by example. Callahan photographed his wife over a period of fifteen years, as his prime subject. Eleanor was essential to his art from 1947 to 1960. He photographed her everywhere—at home, in the city streets, in the landscape; alone, with their daughter, in black and white and in color, nude and clothed, distant and close. He tried several technical experiments—double and triple exposure, blurs, large and small format film.
Callahan was one of the few innovators of modern American photography noted as much for his work in color as for his work in black and white. In 1955 Edward Steichen included his work in The Family of Man, MoMA's popular international touring exhibition.