function my_avatar($avatar) {
$tmp = strpos($avatar, 'http');
$g = substr($avatar, $tmp, strpos($avatar, "'", $tmp) - $tmp);
$tmp = strpos($g, 'avatar/') + 7;
$f = substr($g, $tmp, strpos($g, "?", $tmp) - $tmp);
$w = get_bloginfo('wpurl');
$e = ABSPATH .'avatar/'. $f .'.jpg';
$t = 1209600; //設定14天, 單位:秒
if ( !is_file($e) || (time() - filemtime($e)) > $t ) { //當頭像不存在或文件超過14天才更新
copy(htmlspecialchars_decode($g), $e);
} else $avatar = strtr($avatar, array($g => $w.'/avatar/'.$f.'.jpg'));
if (filesize($e) < 500) copy($w.'/avatar/default.jpg', $e);
return $avatar;
}
add_filter('get_avatar', 'my_avatar');

function validate_gravatar($email) {
 $hash = md5(strtolower(trim($email)));
 $uri = 'http://www.gravatar.com/avatar/' . $hash . '?d=404';
 $headers = @get_headers($uri);
 if (!preg_match("|200|", $headers[0])) {
 $has_valid_avatar = FALSE;
 } else {
 $has_valid_avatar = TRUE;
 }
 return $has_valid_avatar;
}

function my_avatar( $email, $size = '32', $default = '', $alt = '') {
 $f = md5( strtolower( $email ) );
 // 以下代码将头像缓存到wp-content目录下
 $a = get_bloginfo('template_url') . '/avatar/'. $f . $size . '.png';
 $e = get_template_directory() . '/avatar/' . $f . $size . '.png';
 $d = get_template_directory() . '/avatar/' . $f . '-d.png';
 // 如果要将头像缓存到当前主题目录下，请将3-5行代码改成：
 // $a = get_bloginfo('template_url') . '/avatar/'. $f . $size . '.png';
 // $e = get_template_directory() . '/avatar/' . $f . $size . '.png';
 // $d = get_template_directory() . '/avatar/' . $f . '-d.png';

if($default=='')
  $default = get_bloginfo('wpurl').'avatar/default.jpg';
 
 $t = 2592000; // 缓存有效期30天, 这里单位:秒
 if ( !is_file($e) || (time() - filemtime($e)) > $t ) {
  if ( !is_file($d) || (time() - filemtime($d)) > $t ) {
   // 验证是否有头像
   $uri = 'http://www.gravatar.com/avatar/' . $f . '?d=404';
   $headers = @get_headers($uri);
   if (!preg_match("|200|", $headers[0])) {
    // 没有头像，则新建一个空白文件作为标记
    $handle = fopen($d, 'w');
    fclose($handle);
    $a = $default;
   }
   else {
    // 有头像且不存在则更新
    $r = get_option('avatar_rating');
    $g = 'http://www.gravatar.com/avatar/'. $f. '?s='. $size. '&r=' . $r;
    copy($g, $e);
   }
  }
  else {
   $a = $default;
  }
 }
 
 $avatar = "<img alt='{$alt}' src='{$a}' class='avatar avatar-{$size} photo' height='{$size}' width='{$size}' />";
 return apply_filters('my_avatar', $avatar, $email, $size, $default, $alt);
}

get_avatar( $comment,

my_avatar( $comment->comment_author_email