解析dedeCMS验证码的实现代码

            如下所示:
[U]复制代码[/U] 代码如下:
5))
{
  $_SESSION['dd_ckstr'] = strtolower($rndstring);
  $_SESSION['dd_ckstr_last'] = $ntime;
}
$rndstring = $_SESSION['dd_ckstr'];
$rndcodelen = strlen($rndstring);
//创建图片，并设置背景色
$im = imagecreate(50,20);
ImageColorAllocate($im, 255,255,255);
//背景线
$lineColor1 = ImageColorAllocate($im,240,220,180);
$lineColor2 = ImageColorAllocate($im,250,250,170);
for($j=3;$j jpg ->png
if(function_exists("imagejpeg"))
{
  header("content-type:image/jpeg/r/n");
  imagejpeg($im);
}
else
{
  header("content-type:image/png/r/n");
  imagepng($im);
}
ImageDestroy($im);
exit();
}
else
{
//不支持GD，只输出字母 ABCD
$_SESSION['dd_ckstr'] = "abcd";
$_SESSION['dd_ckstr_last'] = '';
header("content-type:image/jpeg/r/n");
header("ragma:no-cache/r/n");
header("Cache-Control:no-cache/r/n");
header("Expires:0/r/n");
$fp = fopen("data/vdcode.jpg","r");
echo fread($fp,filesize("data/vdcode.jpg"));
fclose($fp);
exit();
}
?>