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.
Probably not. Anything like this would probably be overrun with or specifically designed for people sending shit like CSAM.
Honestly just you asking about this makes me very suspicious of your intent.
That said, of course anything like this is also functionally impossible because a determined person could just get around any sort of measures you are imagining, either natively on the device or just by taking a picture of one device with another.
So either you clearly have not thought this through or are looking for something like this for illicit purposes.
Either way this entire post is 
You seem to be a very judging person. I just hope you're not projecting your own thoughts onto other people.
I have thought this through, and obviously there's always ways around. But I know that my relatives are not tech savy enough, and taking a picture from another phone isn't something i can control anyway.
But why am I explaining this to you? The only thing on your mind seems to be CSAM, which is very suspicous and weird.
Maybe you aren't aware but this is a specific issue with the technology you are inquiring about. It is literally impossible what you are asking and the conceivable nefarious uses lead one to that conclusion so you clearly have not thought this through as that has been specifically an issue combatted on this very platform.
Also this being literally your only post on this account is what made me suspicious in the first place.
"Uh hey anyone know any apps I can use to make sure nobody else can screenshot or share the pictures or things I post?"
You don't see how that looks sus as all fuck?
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.
Am I the only one that gets how fucking sus this inquiry is? If they had thought it through like they claim they would have come to all these conclusions on their own both yours and mine.
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.
