Tattooing was introduced at Auschwitz in the autumn of 1941, according to the United States Holocaust Memorial Museum’s Encyclopedia of the Holocaust, and at the adjacent Birkenau the next March. They were the only camps to employ the practice, and it is unclear how many people were branded, briefly on the chest and more commonly on the left forearm.

Only those deemed fit for work were tattooed, so despite the degradation, the numbers were in some cases worn with pride, particularly lower ones, which indicated having survived several brutal winters in the camp. “Everyone will treat with respect the numbers from 30,000 to 80,000,” Primo Levi wrote in his seminal memoir, “Survival in Auschwitz,” describing the tattoos as part of “the demolition of a man.”

After the war, some Auschwitz survivors rushed to remove the tattoos through surgery or hid them under long sleeves. But over the decades, others played their numbers in the lottery or used them as passwords.

Dana Doron, a 31-year-old doctor and daughter of a survivor, interviewed about 50 tattooed survivors for the new Israeli documentary “Numbered,” which she directed with Uriel Sinai, a photojournalist; it will make its premiere in the United States next month at the Chicago International Film Festival.

When she asked survivors whether lovers kissed the number as they might a scar, Ms. Doron said, “some of them looked at me like, ‘What are you nuts?’ and some of them said, ‘Of course.’ ”

“To me, it’s a scar,” said Ms. Doron, who grew interested in the numbering while drawing blood from a tattooed arm in an emergency room. “The fact that young people are choosing to get the tattoos is, in my eyes, a sign that we’re still carrying the scar of the Holocaust.”