PHP & CURL EXPERT NEEDED TO SOLVE: CAPTCHA session reuse attack detected

class Captcha {
        public static function getRecaptcha($recaptchaURL, $referer) {
                $http = new HTTP(false);
                $captcha_js = $http->GET($recaptchaURL, $referer);
                //echo $captcha_js;
                $l = explode("\n",$captcha_js);
                 foreach ($l as $ln) {
                        if (is_int(strpos($ln, 'challenge'))) {
                                $r['challenge'] = substr($ln, strpos($ln, "'")+1, strrpos($ln, "'")-strpos($ln, "'")-1);
                        }
                        if (is_int(strpos($ln, 'server :'))) {
                                $r['server'] = substr($ln, strpos($ln, "'")+1, strrpos($ln, "'")-strpos($ln, "'")-1);
                        }
                }
                $r['filename'] = '/tmp/'.md5(time().rand(1000,9999)).'.jpg';
                //Logger::log("ReCaptcha Challenge: {$r['challenge']}");
                $http->GETFILE($r['server'].'image?c='.$r['challenge'], $r['filename'], $referer);
                Logger::log("ReCaptcha downloaded");
                return $r;
        }
        public static function deathByCaptcha($filename) {
                global $conf;
                Logger::log("DeathByCaptcha request verstuurt");
                require_once 'dbc_client.3.php';
                $c = new DeathByCaptcha_client($conf['deathbycaptcha']['login'], $conf['deathbycaptcha']['passw']);
                if ($r = $c->decode($filename, 120)) {
                        Logger::log("DeathByCaptcha solution: {$r[1]}");
                        return $r;
                } else {
                        Logger::log("DeathByCaptcha timeout");
                        return null;
                }
        }
        public static function deathByCaptchaNotCorrect($id) {
                global $conf;
                require_once 'dbc_client.3.php';
                $c = new DeathByCaptcha_client($conf['deathbycaptcha']['login'], $conf['deathbycaptcha']['passw']);
                Logger::log("DeathByCaptcha wrong solution for $id");
                $c->report($id);
        }
}

class HTTP {
        private $cookies;
        private $useproxy;

        public function HTTP($useproxy=true) {
                $this->cookies = array();
                $this->useproxy = $useproxy;
        }

        public function POST($url, $postdata, $ref=null) {
                $postdata = http_build_query($postdata);
                $s = $this->prepareCurl($ref);
                curl_setopt($s,CURLOPT_URL,$url);
                curl_setopt($s,CURLOPT_POST, true);
                curl_setopt($s,CURLOPT_POSTFIELDS, $postdata);
                //Logger::log($url);
                return $this->filterCurlHeader($s);
        }

        public function POSTFILE($url, $postdata, $ref=null) {
                //$postdata = http_build_query($postdata);
                $s = $this->prepareCurl($ref);
                curl_setopt($s,CURLOPT_URL,$url);
                curl_setopt($s,CURLOPT_BINARYTRANSFER, true);
                curl_setopt($s,CURLOPT_POST, true);
                curl_setopt($s,CURLOPT_POSTFIELDS, $postdata);
                return $this->filterCurlHeader($s);
        }
        public function GET($url, $ref=null) {
                $s = $this->prepareCurl($ref);
                //Logger::log($url);
                curl_setopt($s,CURLOPT_URL,$url);
                return $this->filterCurlHeader($s);
        }

        public function GETFILE($url, $filename, $ref=null) {
                $s = $this->prepareCurl($ref);
                $fp = fopen($filename, "wb");
                curl_setopt($s, CURLOPT_HEADER, FALSE);
                curl_setopt($s, CURLOPT_URL, $url);
                curl_setopt($s, CURLOPT_FILE, $fp);
                curl_exec($s);
                curl_close($s);
                fclose($fp);
        }

        private function prepareCurl($ref) {
                $useragent = "Mozilla/5.0 (Windows; U; Windows NT 6.1; nl; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7";
               $s = curl_init();
                $this->setcookies($s);
                curl_setopt($s,CURLOPT_HTTPHEADER,array('Expect:'));
                curl_setopt($s,CURLOPT_USERAGENT,$useragent);
                if ($this->useproxy) curl_setopt($s,CURLOPT_PROXY,"localhost:8118");
                if (isset($ref)) curl_setopt($s,CURLOPT_REFERER, $ref);
                //curl_setopt($s,CURL_COOKIEJAR, dirname(__FILE__)."/cookie.txt");
                curl_setopt($s,CURLOPT_AUTOREFERER, true);
                curl_setopt($s,CURLOPT_FOLLOWLOCATION, true);
                curl_setopt($s,CURLOPT_MAXREDIRS, 5);
                curl_setopt($s,CURLOPT_RETURNTRANSFER, true);
                curl_setopt($s, CURLOPT_HEADER, true);
                return $s;
        }
        
        private function setcookies($s) {
                if (sizeof($this->cookies) == 0) return;
                foreach($this->cookies as $var => $val) {
                        $tmp[] = "$var=$val";
                }
                $cookiestring = implode(";", $tmp);
                curl_setopt($s, CURLOPT_COOKIE, $cookiestring);
        }
        private function filterCurlHeader($s) {
                $c = curl_exec($s);
                curl_close($s);
               $tmp = explode("\r\n\r\n", $c);
                $header = $tmp[0];
                array_shift($tmp);
                $content = implode("\r\n\r\n", $tmp);
                $lines = explode("\n", $header);
                foreach ($lines as $line) {
                        if (is_int(strpos($line, "Set-Cookie:"))) {
                                $tmp = explode(":", $line);
                                $tmp = explode(";", $tmp[1]);
                                list($var,$val) = explode("=", trim($tmp[0]));
                                $this->cookies[$var] = $val;
                        }
                }
                return $content;
        }
        public function getCleanHTMLDOM($t) {
                $tidy = tidy_parse_string($t);
                $tidy->cleanRepair();
                $dom = DOMDocument::loadHTML($tidy);
        }
}

class Logger {
        public static function log($msg) {
                $c = debug_backtrace();
                $c = strtolower($c[1]['class']);
                if (empty($c)) $c = "main";
                $time = date("H:i:s");
                echo "[$time::$c] $msg\n";
                //DB::log($c ,$msg);
        }
}