Changing the default meta image for sharing purposes

I realize that this might not be covered in the forums, but I was hoping you might help.... In EasyBlog, if there is no image in the blog, I was hoping to use the user's avatar as the default image for og:image. I tried altering the classes/facebook.php with this:

$source = $this->fetch( 'blog.avatar.php' , array( 'row' => $row ) );

That didn't seem to work. Is there a way to call the avatar for that particular blog?

Thanks!