/**
* Class humanized captcha (hc)
* captcha making sense in forms
*
*/
session_start();
class hc{
var $question;
var $answer;
var $options;
var $options_html;
var $session;
var $hash_answer;
public function __construct($question = NULL, $answer = NULL, $options = NULL)
{
$this->session = "humanized_captcha"; //uniqid(md5(microtime()), true);
$this->answer = $answer;
$this->options = $options;
$this->question = $question;
$_SESSION["hc"] = $this->session;
$_SESSION[$this->session]["question"] = $question;
$_SESSION[$this->session]["answer"] = $answer;
$_SESSION[$this->session]["options"] = $options;
$_SESSION[$this->session]["hash"] = uniqid(md5(microtime()), true);
print_r($_SESSION);
 
}
public function show()
{
$this->options_html[] = $this->answer;
foreach($this->options as $opt)
{
$this->options_html[] = $opt;
}
shuffle($this->options_html);
print_r($this->options_html);
$html[] = "<span id=\"captcha_question\">" . 
htmlentities($this->question) . 
"</span>\n<div id=\"captcha_answers\">\n";
foreach($this->options_html as $ans)
{	// (($ans == $this->answer)? ($_SESSION[$this->session]["hash"])
// (uniqid(md5(microtime()), true))
$html[] = "<span class=\"captcha_option\"><label>
<input type=\"radio\" name=\"captcha_option\" value=\"" . 
(($ans == $this->answer)? ($_SESSION[$this->session]["hash"]) : 
(uniqid(md5(microtime()), true)) ) . "\" />" . 
htmlentities($ans) . "</label></span>\n";
}
$html[] = "</div>";
return implode("", $html);
}
public function validate()
{
$return = empty($_GET["captcha_option"])? 
$_POST["captcha_option"] : $_GET["captcha_option"];
if ($return != $_SESSION["humanized_captcha"]["hash"])
{
echo "Invalid code";
}
else
{
echo "Valid code";
}
}
public function __destroy()
{
unset($_SESSION[$this->session]);
}
 
}

include_once("captcha.class.php");
<style>
#captcha_question, #captcha_question, .captcha_option
{
display: block;
}
</style>
<form action = "form01.php" method="post">
<?php
if(!isset($_GET["captcha_option"]) & !isset($_POST["captcha_option"])){
$hc = new hc("Qual o nome do mamífero", "hipopótamo", array("vermelho", "cômodo", "vértebra", "educação"));
echo $hc->show();
} else {
hc::validate();
}
?>
<input type="submit">
</form>