for
(
$i
=0;
$i
<4;
$i
++)
$rndstring
.=
chr
(mt_rand(65,90));
$img_height
=45;
//先定义图片的长、宽
$img_width
=10;
//如果支持 GD,则绘图
if
(function_exists("imagecreate"))
{
//Firefox 部份情况会多次请求的问题,5 秒内刷新页面将不改变 session
$ntime
= time();
if
(
empty
(
$_SESSION
['dd_ckstr_last']) ||
empty
(
$_SESSION
['dd_ckstr']) || (
$ntime
-
$_SESSION
['dd_ckstr_last'] > 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(46,20);
ImageColorAllocate(
$im
, 240,243,248);
//干扰线