Custom Gravatar
<?php
//* Do NOT include the opening php tag shown above. Copy the code shown below.
//* Create a custom Gravatar
add_filter( 'avatar_defaults', 'sp_custom_gravatar' );
function sp_custom_gravatar ($avatar) {
$custom_avatar = get_stylesheet_directory_uri() . '/images/gravatar.png';
$avatar[$custom_avatar] = "Custom Gravatar";
return $avatar;
}