Images not being displayed in social shared messages.

When sharing posts/ pages on social websites, images are not being displayed. I have wordpress SEO and hotlinking protection enabled if that plays any role. FB’s object debugger shows “The ‘og:image’ property should be explicitly provided, even if a value can be inferred from other tags”. How should I rectify this- I have featured images on my twentyfourteen themed website? The problems is the same for twitter and Google+. Althought there are many similar questions asked before, I have not found an understandable solution.