International Holocaust Remembrance Day is marked every year on 27 January, the anniversary of the liberation of Auschwitz-Birkenau in German-occupied Poland, where around 1.5 million people, most of them Jews, were murdered by the Nazis between 1940 and 1945.

Identification snapshots of Auschwitz prisoners that were found in the camp after its liberation Yad Vashem Photo Archives

Set up in 1940 by occupying Nazi forces near the town of Oswiecim – in what is now southern Poland but was then German-occupied territory – as a labour camp for Poles, Auschwitz gradually became the centrepiece of Nazi Party dictator Adolf Hitler's "final solution" plan to exterminate the Jews.

Men, women and children – mostly Jewish but also Gypsies, Russians, Poles and gay people from all over Nazi-occupied Europe – were transported to Auschwitz in overcrowded cattle trains. Many died of hunger and suffocation during the journey which usually lasted days.

When they arrived at the camp, they faced a selection process. SS doctors decided which prisoners were suitable for labour and which should be killed immediately. The elderly and women with children were killed in the camp's gas chambers using the pesticide Zyklon B.

The scale of the industrialised killing at the camp, the cruelty of the guards and the pseudo-medical experiments conducted on prisoners by Nazi doctors have made Auschwitz synonymous with a coldly efficient genocide and total degradation of humanity.

Most of the following images come from the Auschwitz Album, the only surviving visual evidence of the process leading to the mass murder at Auschwitz-Birkenau. It is a unique document and was donated to Yad Vashem by Lilly Jacob-Zelmanovic Meier. The photos were taken at the end of May or beginning of June 1944, either by Ernst Hofmann or by Bernhard Walter, two SS men whose task was to take ID photos and fingerprints of the inmates (not of the Jews who were sent directly to the gas chambers). The photos in the album show the entire process except for the killing itself.

Bodies waiting to be burned in an outdoor fire pit. This is one of four blurred photographs taken secretly in August 1944 inside Auschwitz. The images were taken by an inmate usually named only as Alex, a Jewish prisoner from Greece who was a member of the Sonderkommando – inmates forced to work in and around the gas chambers Public domain

Those who survived the selection process were stripped of their clothes, belongings and identity, and had a number tattooed on their arm. They were issued with striped uniforms and marched to rows of accommodation blocks to begin their lives in the camp.

Living in vastly overcrowded barracks, prisoners survived on extremely low food rations. "Buna-suppe" – a watery soup – was served as a minimal supplement to endure the intolerable working conditions. Prisoners performed various kinds of labour, inside and outside the camp boundaries, working 11 hours a day.

A picture taken in April 1945 depicting the Auschwitz concentration-camp gate, with the inscription 'Arbeit macht frei' AFP
The Auschwitz II-Birkenau, as seen here in a breakdown and timeline, was built to ease congestion in the main camp
Auschwitz aerial photo
An aerial photo of Auschwitz I taken on 25 August 1944 showing a line of new arrivals being registered. It also shows the location of a gas chamber, crematorium and execution wall US National Archives

In mid-January 1945, as Soviet forces approached the Auschwitz concentration camp complex, the SS units began to evacuate prisoners from the camp, in an attempt to delete the evidence. Nearly 60,000 prisoners were marched west from Auschwitz I, Auschwitz-Birkenau and Monowitz. In below freezing temperatures, prisoners, mostly wearing little more than thin uniforms and wooden clogs, were forced to make their way through several feet of snow. Anyone who lagged behind or collapsed was shot. As many as 15,000 prisoners died during the evacuation marches from execution, starvation or exposure.

Auschwitz was liberated by the Soviet Red Army on 27 January 1945. Around 200,000 inmates survived.

The body of a female prisoner lying in the snow when Auschwitz was liberated by the Russians in January 1945 Reuters
Bodies of prisoners are seen lying in the Nazi Auschwitz death camp shortly after it was liberated Reuters

The 73rd anniversary of the liberation of the Auschwitz-Birkenau concentration and extermination camp is commemorated every year on 27 January, as International Holocaust Remembrance Day.