I nowadays prefer to post content on my own site instead of social media if possible, in order to keep the control of my content and use a layout that I actually like instead of just whatever the social media provides me, including to use a permalink of my choice instead of letting the social network use a clunky and numerical URL.
When I post something on my site, and then I re-publish the same content in a social media platform, such as Twitter, YouTube or Instagram, I try to link duplicates using link tags. So, if I post a photo to my site, and then I post the same photo in Twitter, I try to add links on both sides to signal search engines that these two pages have the same content because they are the same concept. You can learn more about POSSE by clicking here.
Sometimes I don’t link to my website in my tweets or in similar content. This usually means that either; a) I forgot, b) I didn’t care enough to do a bidirectional binding, c) I’m doing PESOS, which is the opposite strategy: post in a social network, and then collect foreign posts into your site. If the social network doesn’t allow to edit old posts, I’m unable to add a link to the same content representation hosted in my site. However, I still add a link to the original item shared in a social network when the post is collected in my site.
Either way, these links only signal intentionally duplicated content in other social networks.