这是我使用的工作代码

$dest = imagecreatefrompng('mapCanvas.png');
$src = imagecreatefromjpeg('si.jpg');
imagealphablending($dest, false);
imagesavealpha($dest, true);
// Copy and merge
imagecopymerge($dest, $src, 17, 13, 0, 0, 60, 100, 100);

// Output and free from memory
header('Content-Type: image/png');
imagepng($dest);

imagedestroy($dest);
imagedestroy($src);

这是指向示例的链接，该示例会将透明水印叠加在图像上。可能是您的用例，可能是相关的。

http://www.php.net/manual/zh/image.examples.merged-watermark.php

还有一种方法可以加载JPG图像，调整图像大小，打开alpha跟踪以及将图像导出为GD。

雅各布

<?
$png = imagecreatefrompng('./mark.png');
$jpeg = imagecreatefromjpeg('./image.jpg');

list($width, $height) = getimagesize('./image.jpg');
list($newwidth, $newheight) = getimagesize('./mark.png');
$out = imagecreatetruecolor($newwidth, $newheight);
imagecopyresampled($out, $jpeg, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
imagecopyresampled($out, $png, 0, 0, 0, 0, $newwidth, $newheight, $newwidth, $newheight);
imagejpeg($out, 'out.jpg', 100);
?>