The super high resolution photos are taken with a special rig. Details: https://www.dpreview.com/news/1947958268/google-art-camera-uses-robotic-system-to-take-g

The super high resolution photos are taken with a special rig. Details: https://www.dpreview.com/news/1947958268/google-art-camera-uses-robotic-system-to-take-gigapixel-photos-of-museum-paintings https://www.dpreview.com/news/1947958268/google-art-camera-u... From what I recal, the software used for stitching is more like Excel than Photoshop.