If you are a do-it-yourself programmer and you want to know how to add image validation to a form on your web site then this is the article for you. While there are many ways to do this, if you follow these steps, you will learn the easiest way to get the job done. Once you have mastered the example here, you will have all the concepts and experience you need to incorporate the final product into your form on your website.
We will need two files. The first file will create the validation image and incorporate the image in a validation form. Here is the step-by-step code for the first file: verify.php

---BEGINNING OF FILE: VERIFY.PHP---
< ?php
// Create an image where width=200 pixels and height=40 pixels
$val_img = imagecreate(200, 40);
// Allocate 2 colors to the image
$white = imagecolorallocate($val_img, 255, 255, 255);
$black = imagecolorallocate($val_img, 0, 0, 0);
// Create a seed to generate a random number
srand((double)microtime()*1000000);
// Run the random number seed through the MD5 function
$seed_string = md5(rand(0,9999));
// Chop the random string down to 5 characters
// This is the validation code we will use
$val_string = substr($seed_string, 17, 5);
// Set the background of the image to black
imagefill($val_img, 0, 0, $black);
// Print the validation code on the image in white
imagestring($val_img, 4, 96, 19, $val_string, $white);
// Write the image file to the current directory
imagejpeg($val_img, "verify.jpg");
imagedestroy($val_img);
? >

< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd" >
< html >
< head >
< meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" >
< title >Image Verification< /title >
< /head >
< body >
< img src="verify.jpg" height="40" width="200" alt="validation image" / >
< br / >< br / >Type in the validation code from the image. (case sensitive)
< form action="validateform.php" method="post" >
< input name="random" type="text" value="" >
< input type="submit" >
< !-- The validation code will be posted from a hidden form element -- >
< input name="validation" type="hidden" value="< ?php echo $val_string ? >" >
< /form >
< /body >
< /html >
---END OF FILE: VERIFY.PHP---
Now we will create a file that will perform the validation using the POST method:
---BEGINNING OF FILE: VALIDATEFORM.PHP---
< ?php
if ($_POST['validation'] == trim($_POST['random'])){
echo "You are validated";
}else{
echo "Please go back and get validated.";
}
? >
---END OF FILE: VALIDATEFORM.PHP---
 
Copyright 2006 David Picella
Original article and source code for download are available at http://picella.com --The author, David Picella, is a PhD Student at the University of Wisconsin Milwaukee. In addition to his technical articles on technology and Internet subjects, he has written other articles on health care topics in women's health and reproductive care.