[Guide] PHP Simple Image Verification.

index.htm
<form action="check.php" method="post">
<img src="cap.php"><input type="text" name="cap">
<input type="submit" value="Check">
</form>

check.php
<?php
if ($_SESSION['cap'] == $_POST['cap'])
echo "Correct.";
else
echo "Wrong.";
?>

cap.php
<?php
session_start();

$charNum = 6;
for ($i=1;$i<=$charNum;$i++) {
$ran = array(chr(rand(65,90)), rand(1,9));
$captchastr .= $ran[rand(0,1)];
}
$_SESSION['cap'] = $captchastr;
$captcha = imageCreate(150,40);

$backcolor = imageColorAllocate($captcha, 225, 235, 242);
$txtcolor = imageColorAllocate($captcha, 17, 80, 152);

for($i=1;$i<=$charNum;$i++) {
$font = "tahoma";
imagettftext($captcha,rand(14,20),0,($i*20),30,$txtcolor,$font,substr($captchastr,($i-1),1));
}

$ecolor = imageColorAllocate($captcha, 217, 84, 100);
for($i=1; $i<=2;$i++)
imageellipse($captcha,rand(1,150),rand(1,40),rand(40,100),rand(12,25),$ecolor);

for($i=1; $i<=5;$i++)
imageline($captcha, rand(1, 150), 0, rand(1, 150), 40, $txtcolor);

header('Content-type: image/jpeg');
imageJPEG($captcha);
imageDestroy($captcha);
?>