php createimage不会将图像输出到浏览器

你能帮忙吗

<?php

// Create a 200 x 200 image
$canvas = imagecreatetruecolor(200, 200);

// Allocate colors
$pink = imagecolorallocate($canvas, 255, 105, 180);
$white = imagecolorallocate($canvas, 255, 255, 255);
$green = imagecolorallocate($canvas, 132, 135, 28);

// Draw three rectangles each with its own color
imagerectangle($canvas, 50, 50, 150, 150, $pink);
imagerectangle($canvas, 45, 60, 120, 100, $white);
imagerectangle($canvas, 100, 120, 75, 160, $green);

// Output and free from memory
header('Content-Type: image/jpeg');

imagejpeg($canvas);
imagedestroy($canvas);

?>

使用XAMPP，我得到了localhost/drawrectangle.php，其中包含以下不呈现图像的代码，我得到的是一个图像占位符，您能提供帮助吗

<?php

// Create a 200 x 200 image
$canvas = imagecreatetruecolor(200, 200);

// Allocate colors
$pink = imagecolorallocate($canvas, 255, 105, 180);
$white = imagecolorallocate($canvas, 255, 255, 255);
$green = imagecolorallocate($canvas, 132, 135, 28);

// Draw three rectangles each with its own color
imagerectangle($canvas, 50, 50, 150, 150, $pink);
imagerectangle($canvas, 45, 60, 120, 100, $white);
imagerectangle($canvas, 100, 120, 75, 160, $green);

// Output and free from memory
header('Content-Type: image/jpeg');

imagejpeg($canvas);
imagedestroy($canvas);

?>

你到底得到了什么？右键单击占位符“保存图像”，然后将文件加载到文本/十六进制编辑器中，查看其中的内容。如果有任何php错误/警告被输出，它们将嵌入到图像数据的开头，并导致图像数据被视为已损坏。@KristerAndersson如果header（）之前有任何输出，php将抛出错误。您应该在此处检查并输出它。请参阅“注意：JPEG支持仅在PHP是根据GD-1.8或更高版本编译的情况下可用。”也许您没有启用GD库（PHP扩展）？