$captcha=$_POST["captcha"];
$ver=$_SESSION["captcha"];

$captcha=$_POST["code"];
$ver=$_SESSION["itog"];

<span style="vertical-align: middle;">
<form method="post" action="vls.php?view=ok&ds=clicked" style="padding-top: 5px; vertical-align: middle;">
<img src="captcha.php" align="middle"> <input type=text value='' size=10 maxlength=3 name="captcha">
  <input type="submit" value="Подтвердить просмотр">
</form>
</span>
<?
mysql_close($con);
exit();
}
}
if(!isset($_GET["ds"]) or ($_GET["ds"]=='clicked' and $ver==$captcha))

<span style="vertical-align: middle;">
<form method="post" action="vls.php?view=ok&ds=clicked" style="padding-top: 5px; vertical-align: middle;">

<?php
$a = rand(1,20);
$b = rand(1,20);
$_SESSION["itog"] = $a + $b;
?>

Введите ответ: <?=$a ?> + <?=$b ?> = </b><input type="text" size=5 maxlength=2 name="code">
      <input type="submit" value="Подтвердить просмотр">

</form>
</span>
<?
mysql_close($con);
exit();
}
}
if(!isset($_GET["ds"]) or ($_GET["ds"]=='clicked' and $ver==$captcha))