Programming PHP

The series of requests sent by the web browser for this page looks something like this:
GET /page.html HTTP/1.0
GET /image1.jpg HTTP/1.0
GET /image2.jpg HTTP/1.0
The web server sends back a response to each of these requests. The Content-Type
headers in these responses look like this:
Content-Type: text/html
Content-Type: image/jpeg
Content-Type: image/jpeg
To embed a PHP-generated image in an HTML page, pretend that the PHP script that
generates the image is actually the image. Thus, if we have image1.php and image2.
php scripts that create images, we can modify the previous HTML to look like this:
Example Page
This page contains two images.
Instead of referring to real images on your web server, the img tags nowrefer to the
PHP scripts that generate the images.
Furthermore, you can pass variables to these scripts, so instead of having separate
scripts to generate the two images, you could write your img tags like this:
Then, inside image.php, you can access $_GET['num'] (or $num, ifregister_globals is
on) to generate the appropriate image.
The GD Extension
Before you can start generating images with PHP, you need to check that you actually
have image-generation capabilities in your PHP installation. In this chapter we’ll
discuss using the GD extension, which allows PHP to use the open source GD graphics
library available from http://www.boutell.com/gd/.
Load the familiar phpinfo( ) page and look for a section entitled “GD”. You should
see something similar to the following.
gd
GD Support enabled
GD Version 2.0 or higher
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