is there any reference of photography documenting sex slaves during ww11?

Answer 1

yes, there are such photos. however they do not show actual acts, only references to the women involved with photos of many of them at and in the "comfort rooms and establishments" where they were active in taking the "comfort of the japanese soldiers" to whatever level was desired by the men at the expense of humanity as a people.
the women had to serve as many as thirty or forty a day for months on end without any relief or ability to prevent what was done.
many of those photros are still classified by the allies due to their content and to keep the women from becoming known to the public at large.