the form is a simple captcha but it does not validate the first condition in my if statement

Question

this is the first php script that would get saved as image.php. this is the code:

<?php
$img = imagecreatetruecolor(200,80);

$white = imagecolorallocate($img, 255, 255, 255);
$black = imagecolorallocate($img, 0, 0, 0);
$red = imagecolorallocate($img, 255, 0, 0);
$grey = imagecolorallocate($img,150, 150, 150);
$pink = imagecolorallocate($img, 200, 0, 150);

function randomString($length){
    $chars = "abcdefghijkmnopqrstuvwxyz023456789";
    srand((double)microtime()*1000000);
    $str = "";
    $i = 0;

        while($i <= $length){
            $num = rand() % 33;
            $tmp = substr($chars, $num, 1);
            $str = $str . $tmp;
            $i++;
        }
    return $str;
}

for($i=1;$i<=rand(1,5);$i++){
    $color = (rand(1,2) == 1) ? $pink : $red;
    imageline($img,rand(5,70),rand(5,20), rand(5,70)+5,rand(5,20)+5, $color);
}

imagefill($img, 0, 0, $white);

$string = randomString(rand(2,5));
$_SESSION['string'] = $string;

imagettftext($img, 11, 0, 10, 20, $black, "calibri.ttf", $string);

header("Content-type: image/png");
imagepng($img);
imagedestroy($img);
?>

in the above code everything works....now i create a new php script and name it captcha.php and ill insert this code in the script:

<?php
ob_start();
session_start();
if(!isset($_POST['submit'])){
    echo "<form method=\"post\" action=\"captcha.php\">\n";
    echo "<table border=\"0\" cellspacing=\"3\" cellpadding=\"3\">\n";
    echo "<tr><td>Type The Letters You See Below Into the Box</td></tr>\n";
    echo "<tr><td align=\"right\"><img src=\"image.php\"></td></tr>\n";
    echo "<tr><td align=\"right\"><input type=\"text\" name=\"image\"></td></tr>\n";
    echo "<tr><td align=\"right\"><input type=\"submit\" name=\"submit\" value=\"Check CAPTCHA\"></td></tr>\n";
    echo "</table></form>\n";
}else {
    $image = $_POST['image'];
    if ($image == $_SESSION['string'])
    {
        echo "<b>Great success!</b>\n";
    }
    else 
    {
        echo "<em>Failure!</em>\n";
    }
}
ob_end_flush();
?> 

the past where I'm stuck is on the: if ($image == $_SESSION['string']) it does not validate correctly.

Answer 1

You have to start your session in image.php also.