PHP Form Security Script
This script displays an image of a number that the user must type in correctly before they submit data from a form. The idea is to stop robots easily abusing your services such as automated posts to blogs and forums such as comment spam.
The main script generates an image of a random number and stores the number value in a session varaible. The code that runs after the form data is submitted, compares the number entered by the user with the number stored in the session variable to determine if a human rather than a robot submitted the form.
Save this code as gateway-image.php:
<?php
session_start();
$number = rand(1,999); //generate a random integer
$_SESSION['number'] = $number; //store in session variable
$img_number = imagecreate(40,25);
$backcolor = imagecolorallocate($img_number,0xcc,0xcc,0xcc);
$textcolor = imagecolorallocate($img_number,255,255,255);
imagefill($img_number,0,0,$backcolor);
imagestring($img_number,10,5,5,$number,$textcolor);
header("Content-type: image/jpeg");
imagejpeg($img_number);
?>
Save this code as gateway.php (the html page with the form ):
<?php session_start(); ?> <html> <head> <title>Gateway</title> </head> <body> Please enter the value you see below:<br /> <img src="gateway-image.php" /> <form action="" method="post"> <input type="text" name="number" value="" /><br /> <button type="submit">Submit</button> </form> <?php if (isset($_POST['number'])) if ($_SESSION['number'] == $_POST['number']) echo "Correct"; else echo "Wrong value entered!"; ?> </body> </html>
