With the outbreak of World War II, she took up documentary photography and began to photograph and document social subjects during the duration of the German and Italian occupation of Greece.
[1] She turned her camera to troops departing for the front line, and to the casualties of war, raising awareness of the various humanitarian issues such as the Great Famine which arose out of the occupation.
[1] As Athens suffered a starvation crisis, Papaïoannou photographed emaciated children, providing an account of the horrors of war on the civilian population.
Papaïoannou's attention toward the hardships of the Greek population was not in the least romantic or touristic, but instead honestly portrayed them as proud and independent, optimistic for the future despite poverty.
Her work reflects the dominant representational paradigm of 'humanist photography' prominent in postwar Europe.