PHP includes a large number of free and open source libraries with the core build. PHP is a fundamentally Internet-aware system with modules built in for accessing FTP servers, many database servers, embedded SQL libraries such as embedded MySQL and SQLite, LDAP servers, and others. Many functions familiar to C programmers such as those in the stdio family are available in the standard PHP build.
The GD Graphics Library for dynamically manipulating images. You will need to compile PHP with the GD library of image functions for this to work.
However Ubuntu (and Debian) comes with package called php5-gd
Just type following command to install this module:
# apt-get install php5-gd
$ sudo apt-get install php5-gd
# /etc/init.d/apache2 restart
Test your php application.