iCloud & iCloud Photos · iCloud on the web, Windows and other apps
How do I download original photos from iCloud.com?
Short answer: Sign in at iCloud.com, open Photos, select photos and download them, choosing Unmodified Original for full quality. It's best for small batches; for a whole library use Photos on a Mac or request a copy of your data from Apple.
Sign in at iCloud.com, open Photos, select the photos and use the download button. To get full-quality files, choose the download option for Unmodified Original if it's offered. The files land in your browser's Downloads folder, which you can point at an external drive.
The website suits small batches. For a whole library, it's easier to let Photos on a Mac download originals, or to request a full copy of your data from Apple — see requesting a copy of your iCloud data.