To enable GD-support configure PHP --with-gd[=DIR], where DIR is the GD base install directory. To use the recommended bundled version of the GD library configure --with-gd. In Windows you'll include php_gd2.dll as an extension in php.ini. There is also php_gd.dll for GD1 but it's not preferred.

Enhance the capabilities of GD to handle more image formats by specifying the --with-XXXX configure switch to your PHP configure line.