Hi Max,
Thank you for the information. The error message "Fatal error: Call to undefined function imagecreatefromstring() in /home/accessus/public_html/mywebsite.com/moodle/lib/gdlib.php on line 290" demonstrates that you do not have the GD Library installed / enabled as stated when you installed Moodle:
And documented on: http://docs.moodle.org/25/en/admin/environment/php_extension/gd.
Installing the library will rectify the problem.
Gareth