GD Not installed While Installation

While installing Prestashop I got this error GD Not Installed

First question that arises when I saw this error was what is GD.
The GD library is a graphics drawing library that provides tools for manipulating image data. In Shopp, the GD library is used to process images for generating gallery preview and thumbnail size images automatically.

Next question was how to check if it is installed on my server or not
Ans: make a php file and add code stating

<?php phpinfo(); ?>
and upload it on your server .

if this  comes on the page after php configuration then gd is installed .
If your web hosting does not have GD support you have a limited amount of options:
Contact your web hosting technical support and request support for the GD library in PHP. This is not always successful. Some hosts may be resistant to adding new software due to support costs (maintaining updates) and fear of security threats. This is just a warning that your mileage may vary. Our recommendation… ask really nicely.
Find a new web hosting company that you can be sure fits all the requirements for your Shop.

if you have your own servers it would depend according to your OS.
On Windows servers, php_gd2.dll is included in a standard PHP installation, but is not enabled by default. To enable it, uncomment the extension=php_gd2.dll line in your php.ini file (remove the # from the beginning of that line) and restart the PHP extension.
Linux distributions that have package managers can usually find easy installs. For example: yum install php-gd or apt-get install php5-gd Be sure to restart your web server daemon after installing the library.
Compile from source into PHP (meaning you’ll have to re-compile PHP).

If you have WHM Panel
1: Login into WHM -> Software -> EasyApache [Apache Update]

2: During the build profile in step 5 you can find an option of set exhaustive list from where there will be one option of GD Library.
3: Select that option and rebuild the apache.
4: Restart cPanel and http services.