Building GD with Captcha support

Captchas are typically generated by a PHP script that uses GD. AFAIK, this isn't something you compile into GD itself.

To use GD, simply go to WHM -> Software -> Apache Update. Go through to step 5, then click the button for exhaustive options. Under PHP (or if you're doing concurrent PHP, both PHP versions) check the box for GD then proceed with the compile process.