If you are using iCloud Photos, the pictures in iCloud should be the same (give or take) as those on any of your devices that are using iCloud Photos for the same Apple ID. The system will try to keep all photos on all devices - and full-size versions of all photos In iCloud.

Individual devices can be set to “Optimize … Storage,” which gives them permission to substitute lower-quality space-saving local copies for full-size local ones to free up local storage space.

Have you visited the iCloud support page? You should be able to find answers to all things having to do with iCloud there. Good luck!