If you desire privacy, never upload your images to any cloud service that doesn't offer true end-to-end encryption of the data (that is, one where they do not have the key). Use a service where data is only decryptable on your own devices or devices that you personally authorize. Which is, presently, none of the popular services that I'm aware of.
It's even probably the right choice for a popular service to have made.
Full E2E encryption is going to trigger nightmare "I lost all my photos" customer-service stories when people forget their passwords... which is acceptable when you deliberately signed up for a service where security was the selling point, but not great for someone who bought a mass-market phone.
Yep. See the perennial complaint about Signal as a demonstration of that. They don't persist your messages across devices on privacy/security grounds. That's fine, it's why I use it (or one motivation for me to use it). But it's contrary to what many people expect from that kind of service.
