Robert Frank meaning on the mirror idea means that people are going to experience different outcome on the same life situation. Not everyone is going to experience how to tie their shoe, or how to drive a car. We all have different people and things we interact with so we will definitely experience things different. Even though we have different experience we can still relate to the problem. Basically what I am trying to say it that the mirror concept in photographs will have something that is always going to be reflected back into our idea of life. As for the meaning on the window concept from Robert Frank it means that idea of freedom and endless possibilities.
In the photograph with the three females, the mom and her two daughters is a mirror concept from Robert Frank because he is creating a story that is in his head. He created a real life conflict with mom and daughter. Robert is basically making a mirror image on life that could possibility happen to you or not. I would say the mirror concepts are situations that make the viewer stuck on that one area on the photograph as for the window concept it have you wondering about every other subject matter in the photo with a sense of freedom.
In the photograph with the baby running out the house garage is a window concept from Robert Frank before this idea is like you looking out the window and seeing what is real. This window concept is not planned as much in his head. The window concept you can say is him capturing life or things as it is already without much planning and it still have you thinking what is going on. From the images I have seen today from Robert his window images always involve scenery landscapes with a subject matter. The scenery landscape style gives a sense of freedom to the point you wonder what is beyond life in the sky. Robert two window concept photographs I have seen is always giving me perspective and a sense of freedom. It gives me a sense of free thought to analyze the photo any how I want. As for a mirror concept you get one or less possibility on what you can say is going on because most things are planned.