issue with install on ubuntu

hello everybody,

I am a new user of drupal and I have a problem while install.

I have started installation with commande line interface for apache2, PHP5 and Mysql after that, I started server on my browser, I choosed profile and language but after I had this error's message .
I think every extensions are been installed but I seemed not in fact?

Someone have an idea?

this is error message:
PHP extensions Disable
Drupal requires you to enable the PHP extensions in the following list (see the system requirements page for more information):
gd

by ahead, thank's

HDThoreau