In order to keep a large amount of private family pictures, well, private, I am searching for a replacement for photo storage and sharing cloud services like Google Fotos or Apple Fotos.
On the infrastructure side, the system should not use any cloud infrastructure for image storage (although routing, directory servers or similar are fine). I would imagine a P2P system like Syncthing or Resilio Sync as the transport infrastructure. Self-hosting is ok.
On the client side, I am looking for support for various operating systems, ideally not just through a web interface (which invariably are clunky and don't fit into native environments). A great bonus would be if not all of the image collection would need to be present on all connected devices. Having just thumbnails on each device and fetching the full-resolution original on demand, e.g. from a dedicated home server, would be great.
Is there anything that even comes close? Or did the large players conquer that market completely?