Link Preview Tool: I found this tool in Zeit example repository https://github.com/zeit/now-examples and It's quite helpful and Nice if A Blog post or any page don't have any featured image then you can use this tool API.
I'm using this API into DailyHack Meta Tags to preview page screen in all social network link preview
How to use:
It's so simple just pass the URL as endpoint.
It will return you an image of that page. Good new it's Open Source Project. So, you can host this on your own server.