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Enter a random code to make sure I am human


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Sometimes when you complete a form you have to enter a random code of numbers and letters to make sure that you are human.... what is this called and is it done in PHP or some other language?

I have an online order form that we want to look at implementing this and am wondering if this is a complicated process?


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Not really. It is called a captcha and can be used as long as you have the GD library extension installed with PHP (most installations do by default).

The code for this is below. In a file called "captcha.php" which you include where you want to display the actual image put this code:

$IMGVER_TempString = "";
for($i=1; $i<=4; $i++) {
$IMGVER_TempString .= GetRandomChar();

$_SESSION["IMGVER_RndText"] = $IMGVER_TempString;

function GetRandomChar() {


$IMGVER_RandVal = mt_rand(1,3);

switch ($IMGVER_RandVal) {

case 1:
$IMGVER_RandVal = mt_rand(97, 122);
case 2:
$IMGVER_RandVal = mt_rand(48, 57);
case 3:
$IMGVER_RandVal = mt_rand(65, 90);


return chr($IMGVER_RandVal);


echo '<img src="img.php?'.SID.'" border="0" />';

Then you will need another file called "img.php" which generates the random text on the image:

$IMGVER_IMAGE = imagecreate(110,40);

$IMGVER_COLOR_BLACK = imagecolorallocate($IMGVER_IMAGE, 0, 0, 0);
$IMGVER_COLOR_WHITE = imagecolorallocate($IMGVER_IMAGE, 255, 255, 255);


$IMGVER_RandomText = $_SESSION["IMGVER_RndText"];

imagechar($IMGVER_IMAGE, 4, 20, 13, $IMGVER_RandomText[0] ,$IMGVER_COLOR_WHITE);
imagechar($IMGVER_IMAGE, 5, 40, 13, $IMGVER_RandomText[1] ,$IMGVER_COLOR_WHITE);
imagechar($IMGVER_IMAGE, 3, 60, 13, $IMGVER_RandomText[2] ,$IMGVER_COLOR_WHITE);
imagechar($IMGVER_IMAGE, 4, 80, 13, $IMGVER_RandomText[3] ,$IMGVER_COLOR_WHITE);

header("Content-type: image/jpeg");

Then on your form when you test if the form has been submitted also check the captcha matches a text field that you have placed next to it (in this case called "captchaTextField"):

if(isset($_POST['submitButton'])) {
if($_POST['captchaTextField'] == $_SESSION['IMGVER_RndText']) {
// Handle your form here...

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