How to make a local backup of your iCloud Photos synced library

iCloud Photos is a great way to have all your images and videos across all your iCloud-linked devices. Apple lets you select an optimized option for storage, which ensures the full-resolution of your media is uploaded to iCloud and retained there (and accessible via icloud.com) while each end point, like an iPhone or Mac, has just a set of vastly reduced thumbnails. When you want to work with or view the full-sized photo or movie, double clicking or tapping retrieves it. You can have your cake