Here is an outstanding project from the Guardian.
We start with a period photograph, which you can then morph into a modern photograph of the same spot. You can see the change in the area that’s happened since the Civil War. Additionally, there’s an audio file to play from a commentator speaking about the action that happened there and the period photograph for that place.
What I liked best about it is you can move the slide very slowly and stop it at any point, so you can have a combination of the two photographs on the screen with as much or as little of one or the other as you like.
Thanks to my college classmate, Julie Davila, for finding this treasure.