Although the Nazis deported hundreds of thousands of Jewish men and women, for many places where those tragic events happened, no images are known to document the crime. Surprisingly, there's not even photographic evidence from Berlin, the Nazi capital and home to Germany's largest Jewish community.

The lack of known images is important. Unlike in the past, historians now agree that photographs and film must be taken seriously as primary sources for their research. These sources can complement the analysis of administrative documents and survivor testimonies and thus enrich our understanding of Nazi persecution.

As a historian originally from Germany and now teaching in the U.S., I have researched the Nazi persecution of the Jews for 30 years and published 10 books on the Holocaust.

I searched for unpublished images in all the archives I visited during my research. But I have to admit that I—along with many of my colleagues—did not take the gathered visual evidence seriously as a primary source and rather used it to illustrate my publications.