GD does not need to be installed on the server. The GD extension for PHP has to be enabled, though.
Go to your AdminCP, then to the Maintenance section. In there you should have a "View PHP Info" section. Click on that and look at the listings. About 1/3rd the way down the page you should see a section for GD. You should look for the value
GD Support to see if it is enabled or disabled. Most PHP installs have it
enabled.
If you can get the Human Verification Image to appear (the one that looks
like this) then the GD extension is enabled.