Images from Birkenau, 1944.
"The Sonderkommando photographs were taken by members of the Sonderkommando of crematorium V: Alex from Greece (his full name is unknown), Shlomo Dragon and his brother Josel, Alter Szmul Fajnzylberg (known in the camp as Stanisîaw Jankowski), and David Szmulewski.
/---/A note [describing the images] smuggled out of the camp by the political prisoners Józef Cyrankiewicz and Stanisîaw Kîodziãski on September 4, 1944/.../:
Urgent. Send two iron reels of film (2 1/2 x 3 1/2 in.) as soon as possible. It is possible to take pictures. We send you photographs from Birkenau— people who have been gassed. The photograph shows a heap of bodies piled outdoors. Bodies were burned outdoors when the crematorium could not keep pace with the number of bodies to be burned. In the foreground are bodies ready to be thrown on the heap. Another photo- graph shows one of the places in the forest where people were told to undress, allegedly for a bath, but in fact before being driven to the gas chambers. Send a reel as soon as possible. Send the enclosed photographs to Tell."
From The Sonderkommando Photographs by Dan Stone
More about how the images were taken here