admin/environment/php extension/gd
From MoodleDocs
GD extenion for PHP
This extension provides functionality for handling graphics directly from PHP scripts. It supports the PNG, JPEG, XPM formats as well as FreeType/ttf fonts.
Installing
Package names below may vary if using third party package repositories or the PHP version is different from the operating system's default.
Ubuntu
Download and install gd:
sudo apt-get install php-gd
You might need to restart Apache (not necessary):
sudo /etc/init.d/apache2 restart
CentOS
Download and install gd:
dnf install php-gd
You might need to restart PHP-FPM to apply the change in configuration:
systemctl restart php-fpm
If you are unable to find the correct package try searching with:
dnf search 'php*-gd'
