Adding a Simple Math Captcha to your Form in PHP

Math_Captcha

First is we need to create a new session by adding this code:

1	session_start();

Second, we generate the numbers that we will be using for the Math Captcha:

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$num1=rand(1,9); //Generate First number between 1 and 9
$num2=rand(1,9); //Generate Second number between 1 and 9
$captcha_total=$num1+$num2;

Third, we set the Math question into a variable (This his how the question will look like.)

1	$math = "$num1"." + "."$num2"." =";

Fourth, we set the properties of our Match Captcha image.

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$image = imagecreatetruecolor(120, 30); //Change the numbers to adjust the size of the image
$black = imagecolorallocate($image, 0, 0, 0);
$color = imagecolorallocate($image, 0, 100, 90);
$white = imagecolorallocate($image, 0, 26, 26);

Finally, We create the image:

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imagefilledrectangle($image,0,0,399,99,$white);
imagettftext ($image, 20, 0, 20, 25, $color, $font, $math );//Change the numbers to adjust the font-size

header("Content-type: image/png");
imagepng($image);

Save this as captcha.php, here is the full code:

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session_start();

$num1=rand(1,9); //Generate First number between 1 and 9
$num2=rand(1,9); //Generate Second number between 1 and 9
$captcha_total=$num1+$num2;

$math = "$num1"." + "."$num2"." =";

$_SESSION['rand_code'] = $captcha_total;

$font = 'mmobuyit-captcha-fonts/Arial.ttf';

$image = imagecreatetruecolor(120, 30); //Change the numbers to adjust the size of the image
$black = imagecolorallocate($image, 0, 0, 0);
$color = imagecolorallocate($image, 0, 100, 90);
$white = imagecolorallocate($image, 0, 26, 26);

imagefilledrectangle($image,0,0,399,99,$white);
imagettftext ($image, 20, 0, 20, 25, $color, $font, $math );//Change the numbers to adjust the font-size

header("Content-type: image/png");
imagepng($image);

Next step is to create our form and a some validations.

Validation:

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$errors = array();

if ($_POST['registerUser']) {

if (empty($errors) === true) {

if (empty($_POST['captcha_entered'])) {
$errors[] = '<p class = "input-error">Please answer the Captcha Question</p>';
} elseif ($_REQUEST['captcha_entered']!=$_SESSION['rand_code']) {
$errors[] = '<p class = "input-error">Your answer to the Math Question is incorrect.</p>';
}
}
}

Sample Form:

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