What Is GD Library?

GD is an open source library which is mainly used for creating images dynamically like captcha, charts, graphics etc.It is used for creating PNG,JPEG and GIF kind of images.It was developed by Thomas Boutell and is now maintained by Pierre-A.Joye.

Let us create an image or captcha by using GD library.


//set height and width for rectangular image(captcha)
$width =160;
$height =160;

//amount of background noise to add in captcha image
$noise_level = 15;

//generate the random value one at a time by using rand function

//save it in SESSION variable so that data can be carried from one page to another page.

//create the image resource
$img = imagecreatetruecolor($width, $height);
$col1 = imagecolorallocate($img, 30, 180, 40); //color 1
$col2 = imagecolorallocate($img,170, 255, 195);//color 2
$ns = imagecolorallocate($img, 200, 200, 200);//noise color

//fill the image resource with the color 1
imagefill($img, 0, 0, $col1);

//Add the random code of string to the image
imagestring($img, 25, 40, 18, $code, $col2);//imagestring

// Add some noise to the image.
for ($i = 0; $i < $noise_level; $i++) {
for ($j = 0; $j < $noise_level; $j++) {

//tell the browser that this is an image by throwing header() from server side to client side.


//generate the gif image

//destroy the resource of image created

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