The photo album of German photographer Franz Krieger. Photo courtesy of the New York Times

Less than 24 hours. That’s how long it took readers to help identify the mysterious photographer of a recently discovered photo book containing never-before-seen images of Nazi leader Adolf Hitler.

Lens, the New York Times’ photography blog, asked its readers on Tuesday to help solve a World War II photography mystery. A New Jersey fashion industry executive had lent an old book to the blog, asking for help in identifying its photographer. When the Times put the question to its readers, it took less than a day for the mystery to unravel.

The photographer in question was revealed to be German propaganda artist Franz Krieger, who captured photos of the Eastern Front and of Hitler visiting Hungary. Two readers specifically helped solve the riddle: Harriet Scharnberg, a student of German propaganda photographs, and author Peter Kramml, who, as luck would have it, has actually written a book about Krieger’s work as a Nazi photographer.

The discovered album itself is a work of both art and horror. It manages to show Krieger’s skill in capturing candid, human images of German soldiers, as well as pictures of some of the Third Reich’s first victims in the war. Photographs of Jewish and Russian army prisoners are featured just pages away from unseen portraits of Hitler.

To see more of the photographs, and to read about the mystery of Krieger’s photobook, head to the Lens.