The nextcloud/owncloud debacle seems to need a little more time before sinking too much into it.
We are currently using google drive to sync our photo library w/the home server, and share out private links via email when needed. This keeps us from having to maintain an app/server, users/pws for friends and family...etc, and we can take down the private links as needed.
I think Nextcloud on a VPS or your own server could work? It supports external storage too (S3 etc). Though it's not just for photos.
https://github.com/nextcloud
I'm not sure if they do RAW previews, but should be possible to add.
Koken looks OK too, more photo oriented - http://koken.me/