Right. In principle, it's possible. Apple maintains it can't read your iMessages, for example. And are there any operations that happen on your photos that have

Right. In principle, it's possible. Apple maintains it can't read your iMessages, for example. And are there any operations that happen on your photos that have to happen in the cloud? Thumbnail generation/optimisation can happen during upload. However, since iCloud Photos has a web interface, I imagine they're not doing this.