Many features that you see on the web require that the GD library be enabled on your PHP server. You may need the GD library if you are attempting to display CAPTCHA graphics somewhere on your site.
In a default PHP installation, the GD library should already be enabled.
The following How To explains how to determine if the GD library is enabled on your PHP server, and how you might be able to turn this on.
What Do You Need to Start?
Is GD turned on?
You can check to see if the GD library is enabled by creating a simple phpinfo page on your web server.
1.Create a new file called phpinfo.php
2.Open this file in Notepad, or your preferred WYSIWYG editor such as Dreamweaver.
3.Add the following line of code.
<?php> phpinfo(); <?php>
4.Save your file within your local web server.
5.Open a web browser such as Firefox or Internet Explorer.
6.In the Address bar, enter the URL to this file. Typically, on your local testing server, this will be http://localhost/phpinfo.php
7.If the GD library is enabled, the resulting page should display the following section.
If you don’t see the above section, please refer to the PHP manual for the steps needed to install GD.
Few common examples on how to install GD on different plaform.
Windows Server users
1.Open your PHP.ini file in Notepad, or your preferred WYSIWYG editor. This file is normally located in the C:\Windows\ directory.
2.Locate the following line.
3.Remove the preceding semicolon (;) to enable the option.
4.Save your file.
5.Restart the web server.
Ubuntu Linux users
1.Run the following command to install GD.
sudo apt-get install php5-gd
2.Restart your Apache web server.
Mac OSX users
For Mac OSX users, there is not a simple solution for enabling the GD library after PHP installation is complete.
Instead, we recommend that you use MAMP, which you can obtain from the following location.
MAMP allows you to install Apache, MySQL and PHP for testing your websites locally.