Add photos and videos to Favorites on iCloud.com
In Photos on iCloud.com, open an album or folder to select the photos or videos you want to make a favorite, or double-click a single photo or video.
Click the Favorites icon in the thumbnail to make the photo or video a favorite.
The photo or video is automatically placed in the Favorites album. If you later want to remove the photo or video from your Favorites album, click the Favorites icon in the thumbnail again. The photo or video is automatically removed from the Favorites album, though it remains in iCloud Photos.