Issue with OG Image Tag

I want to hover the image that is in the website in Facebook post http://3ddentalsmile.com, the og:image is set with the proper image link uploaded on server.... but its still showing Facebook icon WHY? I need to get this resolved, same issue in internal pages also...Please help what would be the issue, i checked in facebook debug also

Welcome

Nomoshkar!
Welcome to BHW Saurabh. As for the problem you are facing, it should be because fb bot has cached your domain. Fortunately, it is pretty easy to tell the bot to scrape again. Visit the following URL:

Enter your domain and click on debug, and then click on scrape again button. That should fix it.