经测试代码如下：
<?PHP
/**
* GD2 library，生成缩略图
*
* @param
* @arrange (512.笔记) jb51.cc
**/
function make_thumb($src,$dest,$desired_width)
{
/* read the source image */
$source_image = imagecreatefromjpeg($src);
$width = imagesx($source_image);
$height = imagesy($source_image);
/* find the "desired height" of this thumbnail,relative to the desired width */
$desired_height = floor($height*($desired_width/$width));
/* create a new,"virtual" image */
$virtual_image = imagecreatetruecolor($desired_width,$desired_height);
/* copy source image at a resized size */
imagecopyresized($virtual_image,$source_image,$desired_width,$desired_height,$width,$height);
/* create the physical thumbnail image to its destination */
imagejpeg($virtual_image,83);
}
/*** 来自：编程之家 jb51.cc（jb51.cc） ***/
?>