What does Aunt Eva tell Hannah is the reason that there were no pictures in her family?

Aunt Eva said that no photographs were saved in the death camps.... the only photos they had were carried in their hearts.

But there was something old-fashioned and unfamiliar about this Chaya Abramowicz, something haunting, like one of the old photographs on Grandma Belle's grand piano. Photographs of Grandma's family but none of Grandpa Will's, because, Aunt Eva had once explained, no photographs had been saved in the death camps. "We are our own photos. Those pictures are engraved only in our memories. When we are gone, they are gone."