Tell me about the special snapshot for families if the solider is killed?

I was listening to a story on NPR about a solider who returned with serious brain injuries and they mentioned that his family is one of very few who have a special photo of the solider that is only given to the families if the solider is killed. I'm curious about this photo. When is it taken, what makes it so special (aside from the obvious that it's given on the death of the solider), what becomes of this photo when the solider leaves the military, is it only taken if they are going into combat?