A place to share alternatives to popular online services that can be self-hosted without giving up privacy or locking you into a service you don't control.
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You're basically looking for DRM and I'm not aware of any DRM system that you as a non-media-conglomerate can use.
I'm also not aware of DRM that is actually effective. It's mostly snake oil or, at best, "please don't steal"-signs.
The ultimate Achilles' heel of any DRM system is the analog hole: As soon as the user has an image on their screen, they can take a photo of said screen and share that in any way they want.
As with multi-media piracy, you cannot solve this issue using technology.
You would need a locked down device and be physically present at the viewing. Otherwise they can just take a photo of the photo with their phone and share that.
Maybe this is the solution. If they can't be trusted to behave, they'll be able to see the pictures at the next family gathering.
There is nothing you can do about users taking screenshots.
What most professional photographers do is watermark the low resolution preview pictures, and only genrate download links once paid
Actually, there is plently that can be done against screenshots (plenty apps does that). But someone who takes a photograph of the said phone viewing the picture is a different matter.
There was some discussion about adding DRM Management into the JPEG standard, but I don't believe that actually got implemented.
Signal, Whatsapp, and I think even Snapchat, has view once images. But it's best effort, somebody could certainly take a photo with another phone, or even disable the anti-screenshot feature in the option screen. It just raises the bar.
You may not like this answer but our solution to this is a Google Photos album, locked down so it's invite only. Paired with a social media vigilance keeping an eye out for unauthorized posts. We've only had to treated to kick someone out of the album once. It works well for us. Especially at family events, people post the photos they take too so we have access and they now know not to post on social media.