How to stop 3rd party to reach to a image by a page rule?

I use any image within the article to be to the featured image and thumbnail. but if there is no image within the article, which there is no featured image and thunmail, and if I share the post to social media, social media will use the image on my sidebar as thumbnail. How to set up a rule page that stop them capturing images on the sidebar when sharing to social media while it can be shown to visitors when they are on the website?