Error

You are trying to install Drupal 7, but during the installation at "Verify requirements" step, Drupal returns the following error message

PHP extensions Disabled Drupal requires you to enable the PHP extensions in the following list (see the system requirements page for more information): gd

Cause

The cause of that error is the GD module for PHP is not installed on your server. That GD module for PHP is required by Drupal 7.

Resolution

To fix this choose one of the following four options. Depends on your operating system.

Option 1: Debian 9 Stretch. PHP 7.x.

1. Using Terminal as Root, run the following command on your server
   apt-get install php7.0-gd
2. The "web server config" will automatically be reloaded. Try to install Drupal again.
   If still not working try to reboot your server. Then try again to install Drupal.
3. Done. Enjoy :)

Option 2: Debian 8 Jessie. PHP 5.x.

1. Using Terminal as Root, run the following command on your server
   apt-get install php5-gd
2. The "web server config" will automatically be reloaded. Try to install Drupal again. If still not working try to reboot your server.
3. Done. Enjoy :)

Option 3: Debian 7 Wheezy. PHP 5.x.

1. Using Terminal as Root, run the following command on your server
   apt-get install php5-gd
2. The "web server config" will automatically be reloaded. Try to install Drupal again. If still not working try to reboot your server.
3. Done. Enjoy. Thanks to parvind87 for this fix :)

Option 4: Ubuntu 14.04 Trusty Tahr. PHP 5.6.

1. Using Terminal as Root, run the following command on your server
   apt-get install php5.6-gd
2. The "web server config" will automatically be reloaded. Try to install Drupal again.
   If still not working try to reboot your server. Then try again to install Drupal.
3. Done. Enjoy. Thanks to vindesh for this fix :)