Saw this film yesterday on Netflix. I was very impressed. It is based on true events that happened in Mauthausen Concentration Camp, in particular the story of Francisco Boix, a Spanish prisoner working in the camp's photographic shop. He is obsessed with collating and hiding the negatives of photos he has taken of the various atrocities that take place almost on a daily basis. His objective is that they will be used as evidence if, and when, the camp is liberated and war crimes trials ensue.
The acting is excellent, and the camp scenes reflect the horror of camp life quite graphically. I have visited Mauthausen and am pretty sure that filming was done there. For anyone who has an interest in this period of history,this film may very fill in some gaps in your knowledge of the camp system. Historically, I could not fault it.