Try this code in your custom plugin:
PHP Code:
if ($vbulletin->userinfo['userid'])
{
require_once('./includes/functions_user.php');
$ava_url = fetch_avatar_url($vbulletin->userinfo['userid']);
$avatar = $ava_url[0];
if (!avatar)
{
$ava_url[0] = "images/misc/unknown.gif";
}
$ava_urlX = $ava_url[0];
$nhn_avatar = "<a href=\"profile.php?do=editavatar\"><img src=\"$ava_urlX\" width=\"50\" height=\"50\" border=\"0\" alt=\"Your Avatar\" style=\"vertical-align: middle; margin-right: 5px; margin-top: -4px; border-radius: 5px;-moz-border-radius: 5px;-ms-border-radius: 5px;-o-border-radius: 5px;-webkit-border-radius: 5px;\" /></a>";
$templater = vB_Template::create('header');
$templater->register('nh_avatar', $nhn_avatar);
vB_Template::preRegister('header',array('nhn_avatar' => $nhn_avatar));
$templater->render();
}