php制作验证码

//通过GD库做验证码function verifyImage($type = 1,$length = 4,$pixel = 25, $line = 0,$sess_name = "verify"){    // 创建画布    $width = 80;    $height = 28;    $image = imagecreatetruecolor($width, $height);    $white = imagecolorallocate($image, 255, 255, 255);    $black = imagecolorallocate($image, 0, 0, 0);    // 用填充矩形填充画布    imagefilledrectangle($image, 1, 1, $width - 2, $height - 2, $white);    $chars = buildRandomString($type, $length);//生成随机字符串    $_session[$sess_name] = $chars;        for ($i = 0; $i < $length; $i ++) {        $size = mt_rand(14, 18);        $angle = mt_rand(- 15, 15);        $x = 5 + $i * $size;        $y = mt_rand(20, 26);        $color = imagecolorallocate($image, mt_rand(50, 90), mt_rand(80, 200), mt_rand(90, 180));        $fontfile = "../fonts/SIMYOU.TTF";        $text = substr($chars, $i, 1);       // echo $text;        imagettftext($image, $size, $angle, $x, $y, $color, $fontfile, $text);    }        // 加上干扰元素---点    if ($pixel) {        for ($i = 0; $i < $pixel; $i ++) {            imagesetpixel($image, mt_rand(0, $width - 1), mt_rand(0, $height - 1), $black);        }    }        // 加上干扰元素--线    if ($line) {        for ($i = 0; $i < $line; $i ++) {                        imageline($image, mt_rand(0, $width - 1), mt_rand(0, $height - 1), mt_rand(0, $width - 1), mt_rand(0, $height - 1), $black);        }    }    ob_clean();    // 显示之前要告诉浏览器    header("content-type:image/gif");    // 显示画布    imagegif($image);    // 销毁资源    imagedestroy($image);}