> Photos that are automatically uploaded to iCloud are not scanned?
iCloud backups are not scanned. Only photos uploaded to iCloud Photo Library.
> As for apps - WhatsApp, for example, saves everything to Camera Roll by default. Which then gets auto-uploaded to iCloud.
This is not true at all. The user is asked for explicit permission before apps can save photos to the camera roll, and the user must choose to use iCloud Photo Library.
As for apps - WhatsApp, for example, saves everything to Camera Roll by default. Which then gets auto-uploaded to iCloud.