如何用php生成扭曲及旋转的验证码图片

<?php
function make_rand($length="32"){//验证码文字生成函数
        $str="abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz1234567890";
    $result="";
    for($i=0;$i<$length;$i++){
        $num[$i]=rand(0,61);
        $result.=$str[$num[$i]];
    }
    return $result;
}
$checkcode = make_rand(5);
$im_x=160;
$im_y=32;
function make_crand($length="5") {
    $string = '';
    for($i=0;$i<$length;$i++) {
        $string .= chr(rand(0xb0,0xf7)).chr(rand(0xa1,0xfe));
    }
    return $string;
}
function getauthimage($text , $im_x = 230 , $im_y = 32) {
    $im = imagecreatetruecolor($im_x,$im_y);
    $text_c = imagecolorallocate($im, mt_rand(0,100),mt_rand(0,100),mt_rand(0,100));
    $tmpc0=mt_rand(100,255);
    $tmpc1=mt_rand(100,255);
    $tmpc2=mt_rand(100,255);
    $buttum_c = imagecolorallocate($im,$tmpc0,$tmpc1,$tmpc2);
    imagefill($im, 16, 13, $buttum_c);
    //echo $text;
    $font = 'c://windows//fonts//simsun.ttc';
    //echo strlen($text);
    $text=iconv("gb2312","utf-8",$text);
    //echo mb_strlen($text,"utf-8");
    for ($i=0;$i<mb_strlen($text);$i++)
    {
            $tmp =mb_substr($text,$i,1,"utf-8");
            $array = array(-1,0,1);
            $p = array_rand($array);
            $an = $array[$p]*mt_rand(1,9);//角度
            $size = 20;
            imagettftext($im,$size,$an,10+$i*$size*2,25,$text_c,$font,$tmp);
    }
     $distortion_im = imagecreatetruecolor ($im_x, $im_y);
     imagefill($distortion_im, 16, 13, $buttum_c);
     for ( $i=0; $i<$im_x; $i++) {
         for ( $j=0; $j<$im_y; $j++) {
             $rgb = imagecolorat($im, $i , $j);
             if( (int)($i+20+sin($j/$im_y*2*m_pi)*10) <= imagesx($distortion_im) && (int)($i+20+sin($j/$im_y*2*m_pi)*10) >=0 ) {
                 imagesetpixel ($distortion_im, (int)($i+10+sin($j/$im_y*2*m_pi-m_pi*0.5)*3) , $j , $rgb);
             }
         }
     }
     //加入干扰象素;
    $count = 600;//干扰像素的数量
    for($i=0; $i<$count; $i++){
            $randcolor = imagecolorallocate($distortion_im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
            imagesetpixel($distortion_im, mt_rand()%$im_x , mt_rand()%$im_y , $randcolor);
    }
    $line_c=5;
     //imageline
     for($i=0; $i < $line_c; $i++) {
         $linecolor = imagecolorallocate($distortion_im, 17, 158, 20);
         $lefty = mt_rand(1, $im_x-1);
         $righty = mt_rand(1, $im_y-1);
         imageline($distortion_im, 0, $lefty, imagesx($distortion_im), $righty, $linecolor);
     }
     header("content-type: image/png");
    //以png格式将图像输出到浏览器或文件;
    //imagepng($im);
    imagepng($distortion_im);
    //销毁一图像,释放与image关联的内存;
    imagedestroy($distortion_im);
    imagedestroy($im);
}
?>

<?php
getauthimage(make_crand(5));
?>