You can ask people not to share them, it's up to them if they wanna listen or not. It's hard for me to keep track on who doesn't want their posts shared as I already have lots of other things to do on a daily basis. You're posting them on a public open platform and there's no loss from what I can tell from content on hive being shared outside, if anything it may bring value to our ecosystem that's rewarding you in inflation of all stakeholders (it's kind of one of the base ideas behind inflationary rewards). It may also bring new users to our ecosystem who'll directly follow you and engage/curate your future posts.

I'm not sure what the reason may be why you don't want your photo's shared, maybe consider adding watermarks to them if you think someone might be stealing your photos? I don't think the issue is with sharing, anyone can come in here and share photos/text/other and call it their own outside of hive, whether they're being rewarded for sharing or through other means or just for bragging rights.

Feels like you're going about it the wrong way to ask people not to share pictures when the root issue may be the lack of watermarks on them? Dunno. Kind of a weird situation.