Earlier quoted context omitted.
You mean, directly? I remember seeing a few download links for some images, but many of them aren't directly available (random example: [0]) But otherwise yes, it's one of the best online archive. Wikimedia & some museums's websites are good sources of high-quality material as well. [0]: https://artsandculture.google.com/asset/nicolaas-rubens-wear...
many of the high res images on wikipedia/wikimedia of notable paintings come from this google project (the category for it has ~25,000 https://commons.wikimedia.org/wiki/Category:Files_from_Googl... )
From what I recal, the software used for stitching is more like Excel than Photoshop.