WASHINGTON, Sept. 18 — Last December, Rebecca Erbelding, a young archivist at the United States Holocaust Memorial Museum, opened a letter from a former United States Army intelligence officer who said he wanted to donate photographs of Auschwitz he had found more than 60 years ago in Germany.

Ms. Erbelding was intrigued: Although Auschwitz may be the most notorious of the Nazi death camps, there are only a small number of known photos of the place before its liberation in 1945. Some time the next month, the museum received a package containing 16 cardboard pages, with photos pasted on both sides, and their significance quickly became apparent.

As Ms. Erbelding and other archivists reviewed the album, they realized they had a scrapbook of sorts of the lives of Auschwitz’s senior SS officers that was maintained by Karl Höcker, the adjutant to the camp commandant. Rather than showing the men performing their death camp duties, the photos depicted, among other things, a horde of SS men singing cheerily to the accompaniment of an accordionist, Höcker lighting the camp’s Christmas tree, a cadre of young SS women frolicking and officers relaxing, some with tunics shed, for a smoking break.

In all there are 116 pictures, beginning with a photo from June 21, 1944, of Höcker and the commandant of the camp, Richard Baer, both in full SS regalia. The album also contains eight photos of Josef Mengele, the camp doctor notorious for participating in the selections of arriving prisoners and bizarre and cruel medical experiments. These are the first authenticated pictures of Mengele at Auschwitz, officials at the Holocaust museum said.