Custom Gravatar

// Make a new default gravatar available on the dashboard
function newgravatar ($avatar_defaults) {
 $myavatar ='https://www.example.com/xxx'; // this is the link to the directory where you have saved your custom image.
 $avatar_defaults[$myavatar] = "Custom Avatar";
return $avatar_defaults;
}
add_filter( 'avatar_defaults', 'newgravatar' );