That’s what iCloud is for. Why the need for all the complicated solutions? iCloud is a synchronization service. It’s main purpose is to sync all your data, including photos, across all your devices.

As for photos, it does not alter (compress) the photos. The original, hi-res, images are stored in iCloud and can be downloaded to any device. The default setting is to store lower resolution versions on device to save storage space but as soon as you go to view them the higher res version is downloaded on demand. You can also choose to change the setting to always have the original hi-res version on devices as well with the caveat being that they will take up more space.