Dynamic Image Generation using PHP

Creating images on the fly can be a very useful skill. PHP has some built-in image generation functions, further more, to generate new images or edit existing images on the fly using PHP, we need to have the GD library installed.
In this tutorial we will show you how to get quite interesting and useful effects using image handling functions. We will review two practical tasks: creating security images (captcha) on the fly and building a bar chart using numerical values retrieved from MySQL database.

Creating security images on the fly

At first, have a look at the following script that creates captcha image. Next, we will consider each step of image generation in details.
<?php
//Send a generated image to the browser
create_image();
exit();

function create_image()
{
//Let's generate a totally random string using md5
$md5 = md5(rand(0,999));
//We don't need a 32 character long string so we trim it down to 5
$pass = substr($md5, 10, 5);

//Set the image width and height
$width = 100;
$height = 20;

//Create the image resource
$image = ImageCreate($width, $height);

//We are making three colors, white, black and gray
$white = ImageColorAllocate($image, 255, 255, 255);
$black = ImageColorAllocate($image, 0, 0, 0);
$grey = ImageColorAllocate($image, 204, 204, 204);

//Make the background black
ImageFill($image, 0, 0, $black);

//Add randomly generated string in white to the image
ImageString($image, 3, 30, 3, $pass, $white);

//Throw in some lines to make it a little bit harder for any bots to break
ImageRectangle($image,0,0,$width-1,$height-1,$grey);
imageline($image, 0, $height/2, $width, $height/2, $grey);
imageline($image, $width/2, 0, $width/2, $height, $grey);

//Tell the browser what kind of file is come in
header("Content-Type: image/jpeg");

//Output the newly created image in jpeg format
ImageJpeg($image);

//Free up resources
ImageDestroy($image);
}
?>