The app downloads its on-device art model once (~850 MB — Wi-Fi recommended), and your iPhone compiles it for its Neural Engine on first use. After that, postcards paint in seconds, even offline.
No. Curation, painting, and writing all run on your device. There's no account and no upload — see the privacy policy (it's short, because we collect nothing).
Settings (the gear in your mailbox) lets you delete the art model and the photo reader any time. They re-download when you next need them.
If you granted access to only selected photos, the app can only see those. Add more from the banner on the search screen, or switch to full access in iOS Settings › Privacy › Photos.
Yes — tap the title inside a bundle, or long-press a bundle in the mailbox and choose Rename.
We read everything.