Piwik跟踪API返回GIF89

Question

我想我在这里缺少一些基本的东西，但是当我从here尝试这个例子时（根据我的背景）：

<?php 
$piwikTracker = new PiwikTracker( $idSite = {$IDSITE} );

// Specify an API token with at least Admin permission, so the Visitor IP address can be recorded 
// Learn more about token_auth: https://piwik.org/faq/general/faq_114/
$piwikTracker->setTokenAuth('my_token_auth_value_here');

// You can manually set the visitor details (resolution, time, plugins, etc.) 
// See all other ->set* functions available in the PiwikTracker.php file
$piwikTracker->setResolution(1600, 1400);

// Sends Tracker request via http
$piwikTracker->doTrackPageView('Document title of current page view');

// You can also track Goal conversions
$result = $piwikTracker->doTrackGoal($idGoal = 1, $revenue = 42);
?>

$result变量包含

GIF89a�����������!�����,�������D�;

我被告知是一个小型跟踪GIF。但是为什么API会返回跟踪GIF？难道它不应该是关于成功/失败的状态结果吗？