If you are receiving following error message when uploading image via any script (WordPress / Drupal / Joomla / prestashop etc.)
This means your server do not have GD Library installed.
Solution for cPanel Server
If you have root access to server, and you are on a cPanel server, you can install GD from EasyApache from:
WHM Home >> Software >> EasyApache (Apache Update)
Re-run EasyApache and select GD
Solution for non-cPanel server
If you are not on a cPanel server, here is how you can install GD library.
Login to your server as root via SSH and run following command
yum install php-gd service httpd restart
yum install gd gd-devel php-gd service httpd restart
I don’t have root access of server
If you are on a shared hosting or if you do not have root access of server, please contact your hosting provider to enable / install GD library on the server.