Facebook thumbnail share button

I don’t know where to post it so move please.

My doubt is how to change the image when you click in the facebook like or share icon. It uses the default ugly gravatar and i don’t know how to change it to my logo.

Maybe is because i changed the cname of my domain to point to my new website.

What can i do?

thank you

http://andrevicentegoncalves.com/blog/