[php 随机生成验证码]

<?phpsession_start();//随机生成验证码的字符串function random($len) {    $srcstr="abcdefghijklmnpqrstuvwxyz123456789";    mt_srand();    $strs="";    for($i=0;$i<$len;$i++) {        $strs.=$srcstr[mt_rand(0,33)];    }    return ($strs);}$str=random(5); //随机生成的字符串$width=60;  //验证码图片的宽度$height=25; //验证码图片的高度//date in the pastheader("expires:mon,26 jul 1997 05:00:00 gmt");//always modified header("last-modified:".gmdate("d,d m y h:i:s")."gmt");//http/1.1 header("cache-control:no-store,no-cache,must-revalidate");header("cache-control:post-check=0,pre-check=0",false);//http/1.0header("pragma:no-cache");header("content-type:image/png"); $im=imagecreate($width,$height);$back=imagecolorallocate($im,0xff,0xff,0xff);    //背景色$pix=imagecolorallocate($im,187,190,247);        //模糊点颜色$font=imagecolorallocate($im,41,163,238);        //字体色//绘制1000个模糊作用的点mt_srand();for($i=0;$i<1000;$i++) {    imagesetpixel($im,mt_rand(0,$width),mt_rand(0,$height),$pix);}imagestring($im,5,7,5,$str,$font);//绘制随机生成的字符串imagerectangle($im,0,0,$width-1,$height-1,$font);//在验证码图像周围绘制1px的边框imagepng($im);//建立一张png格式图形imagedestroy($im);//将图片handle解构，释于内存空间$_session["auth_code"]=$str;?>

@header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT");//标记内容最后修改时间@header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");//内容过期时间 @header("Cache-Control: no-cache, must-revalidate" );//强制不缓存@header("Pragma: no-cache" );//禁止本页被缓存