[5] During the Occupation, Oorthuys became involved in the Personal Identification Centre established in 1942 and made passport photos for fake ID cards, while earning a bare living on an assignment from Contact [nl] publishing company for a book about agriculture.

The group photographed in any way they could, keeping cameras concealed and shooting 'from the hip'; consequently the quality of the imagery is distinguished by its haphazard nature; often with tilted, uncentered framing and other accidental effects.

[11] Their aim was initially to document the Allies’ liberation which was longer in coming than hoped, and instead they recorded a severe winter of hunger and resistance in photos that have become the image of the German occupation,[12] especially Cas Oorthuys’ picture of a woman with a piece of bread in close-up.

In keeping with his convictions, from January until March 1947, Oorthuys, accompanied by his writer the educationalist Albert de la Court, travelled through Java and Borneo in Indonesia commissioned by ABC-Press and the publishing house Contact.

Photography became a family concern;[5] during the summer holidays from 1951 they travelled to make 28 photo pocketbook [vague] in a series for Contact-Photo books, starting with Bonjour Paris with a cover by Jan van Keulen, each on a different country, promoting tourism for a now more prosperous Dutch population.

[26] The compact books were designed around the square format of the Rolleiflex that Oorthuys favoured and several were marketed by foreign publishers in English, French and German language editions.

At the end of his career he left 500,000 pictures, a huge archive faithfully maintained by his wife Lydia, who sold its imagery to a variety of clients before she donated the entire collection to Nederlands Fotomuseum when she was in her seventies.