Your images would be hidden from social media sites if you use social media locks.
Facebook, Twitter, and Pinterest, for example, use a variety of techniques to make posts more engaging on their sites. When a website address is posted, one of the common strategies is to capture an image to show in the social post.
Facebook & Twitter
If a user posts your website address on Facebook or Twitter, you can use Facebook and Twitter Locks to tell them not to grab a picture from your site. Just enable Facebook Lock and Twitter Lock to do so.
The Cybarmor settings menu's Pinterest Lock feature prevents visitors from saving or "pinning" photos from your site to their Pinterest boards.