I'm using mine as a general cloud storage alternative as well, so it's using a little over 1TB. About a quarter of that is photos. So not too huge, considering they're saving at full resolution.
Nextcloud has https://apps.nextcloud.com/apps/facerecognition which integrates with their CardDav, but I don't think my Pine64 with only 2gb of RAM would be able to run that.
