Generating CAPTCHA Image Using PHP

The CAPTCHA concept is very useful to prevent automated registration. If you have enabled gd library, you can create a captcha code for your registration form using PHP.

Consider the following parts of code, name the file as "captcha.php"

session_start();

if(isset($_SESSION[‘captcha’]))
{
unset($_SESSION[‘captcha’]);
}

The above code will start session and clear the old captcha’s session value if it set.

$num_chars = 5; //number of characters for captcha image
$characters = array_merge(range(0,9),range(‘A’,‘Z’),range(‘a’,‘z’)); //creating combination of numbers & alphabets
shuffle($characters); //shuffling the characters

The above part of code describes the number of captcha characters and total available characters, here I am using all the lower and upper case alphabets and all numerics.
//getting the required random 5 characters
$captcha_text = "";
for($i=0;$i<$num_chars;$i++)
{
$captcha_text .= $characters[rand(0,count($characters)-1)];
}

$_SESSION[‘captcha’] = $captcha_text; // assigning the text into session

This part of code generated the required captcha code in a random manner from the available character array, also It assigns the value to session variable.

header("Content-type: image/png"); // setting the content type as png
$captcha_image = imagecreatetruecolor(140, 30);

$captcha_background = imagecolorallocate($captcha_image, 225, 238, 221); //setting captcha background colour
$captcha_text_colour = imagecolorallocate($captcha_image, 58, 94, 47); //setting cpatcha text colour

imagefilledrectangle($captcha_image, 0, 0, 140, 29, $captcha_background); //creating the rectangle

$font = ‘Arial.ttf’; //setting the font path

imagettftext($captcha_image, 20, 0, 11, 21, $captcha_text_colour, $font, $captcha_text);
imagepng($captcha_image);
imagedestroy($captcha_image);

The remaining code will draw the image.

How to use this captcha?

It’s simple, in your registration form put this part of code:



Then you can put a text box to enter the captcha value, and then you can compare the entered captcha value with the assigned captcha session value.