It never seems to be, actually.
If you see this error, it means the gd extensions to php aren’t installed or active.
Fatal error: Call to undefined function imagecreatetruecolor() in /usr/local/www/data-dist/wordpress/wp-admin/admin-functions.php on line 2192
In FreeBSD, it’s as simple as:
portinstall php5-gd
apachectl restart
YMMV