I have never been able to verify this.
In Pittsburgh I did a lot of "urban exploration" -- old factories, places down town. This old guy took us on a tour of his favorite spots. A brick factory with huge windows.
"They took so many photos during the civil war. Sometimes to identify the dead. After the war no one wanted to see those photos anymore. So, they recycled the glass plates into windows like these."
You didn't look out of those windows, they looked into you.