Single Digit Captcha Match, PHP - php

Question

I run a PTC website advertising websites for people. And i'm needing an easy to to lower or completely prevent bot usage.
After the advertisement counter is done counting down i would like a captcha to load.
But i don't want a captcha that you have to enter anything. Just a single mouse click.
If the captcha can be done in javascript that would be really great.
I'm looking for something sort of like this:
Counter:0 Select Matching Number: 7 [1] [0] [7] [2]
The user would have to click on the number in the box that matches the number.
Digits would be within 1-9.

Answer 1

Short of a full captcha you wont stop a determined bot.
A few ideas.
Allow 10 - 15 requests within 10 a minutes period, if it exceeds that, ask for captcha or block completely. Make sure this is IP based, because cookies/session wont work
Add some javascript to the form so that it cannot be posted without it. Most email collecting spam bots won't run javascript and give up. Generate a random string, store in $_SESSION on page request. Use javascript to add to the form post. if that string doesn't exist match on form post display a captcha.
Or use javascript to contstruct the form itself.
A determined scraper can get around most anything, but you just want to increase the cost of doing so.

Answer 2

I have made a CAPTCHA script. It's size, number of characters, and characters to choose from are customizable.
Here is captcha.php:
<?php
function generateCaptcha($num_digits, $challenge_num, $size, $chars, $incode = false) {
if(session_id() == '') session_start();
if(isset($_SESSION['captcha'])) unset($_SESSION['captcha']);
// You *must* type your own random salt here, *DO NOT* use this one.
$salt = 'H#(*h3^rh#(*E%h$W*WK#vMIv)%(D*(A&*W#A^D6#r4*I%u8tgsc#yejdi$d8dee';
$message = '';
if(isset($_POST['hash']) && isset($_POST['code'])) {
if(!empty($_POST['hash']) && !empty($_POST['code']) && !empty($_POST['correct_index'])) {
if(md5($_POST['hash'] . $_POST['code'] . $salt) == $_POST['correct_index']) {
$message = '<p>Correct!</p>';
} else {
$message = 'Incorrect code. Please try again.';
}
}
}
$code = '';
if($incode == false) {
for($i = 0; $i < $num_digits; $i++) {
$digit = substr($chars, floor(mt_rand(0, strlen($chars) - 1)), 1);
while(strpos($code, "$digit") !== false) {
$digit = substr($chars, floor(mt_rand(0, strlen($chars) - 1)), 1);
}
$code .= $digit;
}
} else {
for($i = 0; $i < $num_digits; $i++) {
$digit = substr($incode, floor(mt_rand(0, strlen($incode) - 1)), 1);
while(strpos($code, "$digit") !== false) {
$digit = substr($incode, floor(mt_rand(0, strlen($incode) - 1)), 1);
}
$code .= $digit;
}
}
$parts = str_split($code);
$width = $num_digits * $size;
$height = $size * 2;
$image = imagecreatetruecolor($width, $height);
$background = imagecolorallocate($image, floor(mt_rand(96, 255)), floor(mt_rand(96, 255)), floor(mt_rand(96, 255)));
imagefilledrectangle($image, 0, 0, $width, $height, $background);
$num_spots = floor(mt_rand($size * 2, $size * 15));
for($i = 0; $i < $num_spots; $i++) {
$color = imagecolorallocate($image, floor(mt_rand(30, 255)), floor(mt_rand(30, 255)), floor(mt_rand(30, 255)));
$x = floor(mt_rand(0, $width));
$y = floor(mt_rand(0, $height));
$ellipse_width = floor(mt_rand(0, $size / 2));
$ellipse_height = floor(mt_rand(0, $size / 2));
imagefilledellipse($image, $x, $y, $ellipse_width, $ellipse_height, $color);
$x1 = floor(mt_rand(0, $width));
$y1 = floor(mt_rand(0, $height));
$x2 = floor(mt_rand(0, $width));
$y2 = floor(mt_rand(0, $height));
imageline($image, $x1, $y1, $x2, $y2, $color);
}
$num_dots = floor(mt_rand($size * 50, $size * 80));
for($i = 0; $i < $num_dots; $i++) {
$color = imagecolorallocate($image, floor(mt_rand(30, 255)), floor(mt_rand(30, 255)), floor(mt_rand(30, 255)));
$x = floor(mt_rand(0, $width));
$y = floor(mt_rand(0, $height));
imagesetpixel($image, $x, $y, $color);
}
for($i = 0; $i < count($parts); $i++) {
$color = imagecolorallocate($image, floor(mt_rand(0, 150)), floor(mt_rand(0, 150)), floor(mt_rand(0, 150)));
$x = floor(mt_rand($size * 0.9, $size * 1.1));
$y = floor(mt_rand($size, $size * 2));
imagettftext($image, $size, floor(mt_rand(-10, 10)), $i * $x, $y, $color, 'Justus-Bold.ttf', $parts[$i]);
imagettftext($image, $size, floor(mt_rand(-10, 10)), $i * $x + floor(mt_rand(1, 7)), $y, $color, 'Justus-Bold.ttf', $parts[$i]);
imagettftext($image, $size, floor(mt_rand(-10, 10)), $i * $x + floor(mt_rand(1, 7)), $y, $color, 'Justus-Bold.ttf', $parts[$i]);
imagettftext($image, $size, floor(mt_rand(-10, 10)), $i * $x + floor(mt_rand(1, 7)), $y, $color, 'Justus-Bold.ttf', $parts[$i]);
}
$white = imagecolorallocate($image, 255, 255, 255);
$filename = md5(time() . $_SERVER['REMOTE_ADDR'] . mt_rand(0, 1000)) . '.png';
imagepng($image, $filename);
imagedestroy($image);
$file = file_get_contents($filename);
$imgsize = getimagesize($filename);
unlink($filename);
$captcha = 'data:' . $imgsize['mime'] . ';base64,' . base64_encode($file);
$challenge = array('captcha' => '', 'code' => null, 'size' => 0, 'digits' => 0);
if($incode == false) {
$challenge = generateCaptcha($challenge_num, 0, $size, $chars, $code);
}
$hash = md5($challenge['code'] . $salt);
$correct_index = array();
for($i = 0; $i < strlen($challenge['code']); $i++) {
$correct_index[] = strpos($code, substr($challenge['code'], $i, 1));
}
$result = array(
'captcha' => $captcha,
'challenge' => array($challenge['captcha'], $challenge['size'], $challenge['digits']),
'size' => array($imgsize[0], $imgsize[1]),
'hash' => $hash,
'code' => $code,
'message' => $message,
'width' => $size,
'digits' => $num_digits,
'correct_index' => md5($hash . implode('', $correct_index) . $salt)
);
return $result;
}
?>
...and here is captcha.html:
<!DOCTYPE HTML>
<!--
<?php
include 'captcha.php';
$captcha = generateCaptcha(4, 2, 100, '0123456789');
?>
-->
<html lang="en-US">
<head>
<meta charset="UTF-8" />
<title>Click-captcha test</title>
<style type="text/css">
#challenge, #captcha-img {
margin: 10px
}
#captcha-img {
overflow: hidden
}
.captcha-digit {
display: block;
float: left;
width: <?php echo $captcha['width']; ?>px;
height: 100%;
cursor: pointer
}
.captcha-digit-selected {
background: #ccc;
opacity: .75;
filter: progid:DXImageTransform.Microsoft.Gradient(StartColorStr='#f2cccccc', EndColorStr='#f2cccccc')
}
</style>
<script type="text/javascript">
var captchaLinks = [];
var digits = [];
var num_digits = <?php echo $captcha['challenge'][2]; ?> - 1;
addEvent(window, 'load', init);
function init() {
captchaLinks = ['<?php
$digits = array();
for($i = 'digit0'; $i < 'digit' . $captcha['digits']; $i++) {
$digits[] = $i;
}
echo implode("', '", $digits);
?>'];
for(var i = 0; i < captchaLinks.length; i++) {
//for(var link in captchaLinks) {
addEvent(document.getElementById(captchaLinks[i]), 'click', newCaptchaDigit);
}
}
function newCaptchaDigit(e) {
if(e.target.className == 'captcha-digit captcha-digit-selected') {
digits.splice(digits.indexOf(e.target.id.substr(-1, 1)), 1);
e.target.className = 'captcha-digit';
} else if(digits.length <= num_digits) {
digits.splice(num_digits, digits.length - num_digits, e.target.id.substr(-1, 1));
e.target.className = 'captcha-digit captcha-digit-selected';
}
document.getElementById('code').value = digits.join('');
}
function addEvent(elem, event, handler) {
if(elem !== null & typeof elem !== 'undefined') {
if(elem.addEventListener) {
elem.addEventListener(event, handler, false);
} else if(elem.attachEvent) {
elem.attachEvent('on' + event, handler);
} else if(elem['on' + event]) {
elem['on' + event] = handler;
}
}
}
</script>
</head>
<body>
<div>
<form action="<?php echo $_SERVER['REQUEST_URI']; ?>" method="post">
<div id="captcha">
<div><?php echo $captcha['message']; ?></div>
<div>Click the following number sequence:
<div id="challenge" style="width: <?php echo $captcha['challenge'][1][0]; ?>px; height: <?php echo $captcha['challenge'][1][1]; ?>px; background-image: url('<?php echo $captcha['challenge'][0]; ?>')"></div>
</div>
<div id="captcha-img" style="width: <?php echo $captcha['size'][0]; ?>px; height: <?php echo $captcha['size'][1]; ?>px; background-image: url('<?php echo $captcha['captcha']; ?>')">
<?php for($i = 'digit0'; $i < 'digit' . $captcha['digits']; $i++) { ?>
<a class="captcha-digit" id="<?php echo $i; ?>"></a>
<?php } ?>
</div>
</div>
<input type="hidden" name="hash" value="<?php echo $captcha['hash']; ?>" />
<input type="hidden" name="correct_index" value="<?php echo $captcha['correct_index']; ?>" />
<input type="hidden" name="code" id="code" value="" />
<input type="submit" value="Submit" />
</form>
</div>
</body>
</html>
Hopefully you will able to see what is going on, but I will explain it here. :-)
The function is called generateCaptcha, and it accepts the parameters $num_digits, $challenge_num, $size, $chars, $incode = false.
$num_digits: number of characters to put in the CAPTCHA
$challenge_num: number of characters to put into the challenge
$size: size of the CAPTCHA
$chars: what characters to include (e.g. for numbers: '0123456789')
$incode: this is just so the script can tell if it has been called by itself to generate the challenge or not. Don't set it.
So to create a CAPTCHA image with 4 characters, a 1 character challenge (like your question), size 30, and only with digits, use this code:
<?php
include 'captcha.php';
$captcha = generateCaptcha(4, 1, 30, '0123456789');
?>
Then the variable $captcha will end up something like this:
array(9) {
["captcha"]=>
string(118058) "data:image/png;base64,iVBORw0KG...kSuQmCC"
["challenge"]=>
array(3) {
[0]=>
string(76266) "data:image/png;base64,iVBORw0KG...kJggg=="
[1]=>
array(2) {
[0]=>
int(200)
[1]=>
int(200)
}
[2]=>
int(2)
}
["size"]=>
array(2) {
[0]=>
int(400)
[1]=>
int(200)
}
["hash"]=>
string(32) "81bc501400b8da366e70b26007cb2323"
["code"]=>
string(4) "4817"
["message"]=>
string(0) ""
["width"]=>
int(100)
["digits"]=>
int(4)
["correct_index"]=>
string(32) "17ae615be69c757505dc7f69fce2afb1"
}
If you need any more information, please ask in a comment.