Facebook link to website logo

I’d recommend checking out the following plugins:

Either one will take care of all of the Open Graph metadata. Once you have the plugin set up, you can simply go to your homepage and you will see a “Featured Image” widget:

Featured Image

Pick your logo and you will see the og:image which is what Facebook uses to set the post image.

<meta property="og:image" content="http://web.site/wp-content/uploads/image.jpg" />

Update

I see that you set up the Open Graph Protocol Framework and now when I visit your website, I see the og:image metadata. Here’s a preview of what it looks like if I were to share it on LinkedIn:

LinkedIn Snippet