禁用wordpress gravatar使用本地头像提高网页打开速度

if ( !function_exists( 'get_avatar' ) ) : 
/** 
* Retrieve the avatar for a user who provided a user ID or email address. 
* 
* @since 2.5 
* @param int|string|object $id_or_email A user ID, email address, or comment object 
* @param int $size Size of the avatar image 
* @param string $default URL to a default image to use if no avatar is available 
* @param string $alt Alternate text to use in image tag. Defaults to blank 
* @return string tag for the user's avatar 
*/ 
function get_avatar( $id_or_email, $size = '96', $default = '', $alt = false ) { 
if ( ! get_option('show_avatars') ) 
return false; 
if ( false === $alt) 
$safe_alt = ''; 
else 
$safe_alt = esc_attr( $alt ); 
if ( !is_numeric($size) ) 
$size = '96'; 
$default = includes_url('images/blank.gif'); 
$avatar = ""; 
return apply_filters('get_avatar', $avatar, $id_or_email, $size, $default, $alt); 
} 
endif;