all free to Captcha[机器码增强]

 function getrandom ($length = 6, $mode = 0){
	switch ($mode) {
	case '1':
	$str = '1234567890';
	break;
	case '2':
	$str = 'abcdefghijklmnopqrstuvwxyz';
	break;
	case '3':
	$str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
	break;
	case '4':
	$str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
	break;
	case '5':
	$str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
	break;
	case '6':
	$str = 'abcdefghijklmnopqrstuvwxyz1234567890';
	break;
	default:
	$str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890';
	break;
	}

	$result = '';
	$l = strlen($str);

	for($i = 0;$i < $length;$i ++){
	$num = rand(0, $l-1);
	$result .= $str[$num];
	}
	return $result;
	}

function pick_word() {
		// set default words

        //by modx.cn

       

       
 
	 	/*
		$words="MODx,Access,Better,BitCode,Chunk,Cache,Desc,Design,Excell,Enjoy,URLs,TechView,Gerald,Griff,Humphrey,Holiday,Intel,Integration,Joystick,Join(),Oscope,Genetic,Light,Likeness,Marit,Maaike,Niche,Netherlands,Ordinance,Oscillo,Parser,Phusion,Query,Question,Regalia,Righteous,Snippet,Sentinel,Template,Thespian,Unity,Enterprise,Verily,Veri,Website,WideWeb,Yap,Yellow,Zebra,Zygote";
        */
        $words="99";
		$words=$this->getrandom(6,6);
		return $words;
		//include "config.inc.php";//MODXCN DEL
		// connect to the database
		/*MODXCN
		if(@$dbConn = mysql_connect($database_server, $database_user, $database_password)) {
			mysql_select_db($dbase);
			$sql = "SELECT * FROM $dbase.".$table_prefix."system_settings WHERE setting_name='captcha_words'";
			$rs = mysql_query($sql);
			$limit = mysql_num_rows($rs);
			if($limit==1) {
				$row = mysql_fetch_assoc($rs);
				$words = $row['setting_value'];
			}
		}

		$arr_words = explode(",", $words);
        */
		/* pick one randomly for text verification */
        /*   MODXCN
		return sprintf("%s",$arr_words[array_rand($arr_words)].rand(10,90));
		*/
	}