When I used iOS last, a few years ago, photos were not considered files. (Yep... let that thought digest for a bit). This made things like SyncThing/Mobius useless. IIRC photos were managed through some separate API for "security reasons".
To access photos on a connected iDevice from a Linux machine, you need iFuse, and even then, iOS presents you all images at once. So your photos, received photos, downloads, screenshots, are all in one big pile. Have fun. Oh, but they are split into folders. By number.