php - GD 库不工作

Question

generate.php 正在工作，但是如果我尝试使用我的 index.php 检索图像，<img src="generate.php"/>我会得到一个空白屏幕。

生成.php

<?php
    header('Content-type: image/png');

    if(isset($_GET['email'])){
        $email = $_GET['email'];
    }else{
        $email = 'No email specified';
    }
    $email_length = strlen($email);

    $font_size = 4;

    $image_height = ImageFontHeight($font_size);
    $image_width = ImageFontWidth($font_size) * $email_length;

    $image = imagecreate($image_width, $image_height);

    imagecolorallocate($image, 255, 255, 255);
    $font_color = imagecolorallocate($image, 0, 0, 0);

    imagestring($image, $font_size, 0, 0, $email, $font_color);
    imagepng($image);
?>

索引.php

Name:<br>
Dave
<br><br>
Email: <br>
<img src="generate.php"/>