iCloud Photos

When you upgrade to macOS Catalina and launch Photos, it’ll import your existing photo library, normally in Pictures in your user account’s home folder in Users on Macintosh HD. If you’re using Optimise Mac Storage to keep low-res copies on your Mac, that’ll stay the same; opening a photo will download the full version. (Everything referring to managing photos here also applies to videos.)

All photos that you shoot, or import into your Camera Roll from sources such as Apple’s Camera Connection Kits, on devices on which iCloud is enabled with your Apple ID