One trap worth handling early: keep the Orientation tag when you strip EXIF, or half the uploads from iPhones will show up sideways on other clients. Order matters for blossom uploads too, hash after stripping and never before. Otherwise the integrity check fails on every image. For the iOS port, HEIC is the default camera format and several Nostr clients still render it badly, so convert to JPEG on the way in. A Flutter codebase that signs through a remote signer will save you most of the key-handling pain later.