I first put together a good-sized library of historical photos that looked like they have potential to be blended. But unfortunately most of these photos end up on the digital cutting room floor because there’s simply no way to get the same photo today because either a building or a tree is in the way. Other potential photos have copyright claims with no way to get a release. Once I get a good location, I get everything lined up just right. My goal is to stand in the exact spot where the original photographer stood. Doing this needs to take into account equivalent focal length and how the lens was shifted. I take plenty of shots, each nudged around a bit at each location. Just moving one foot to the left changes everything.
He has 25 historical stitches completed so far, split between two parts (including a pretty grim photo of a pile of dead horses rotting in front of a Mercedes in part one), with a promise of more on the way.
Here's a couple more shots to get you started: