The "GD Toolkit" module provides a default toolkit to be used by the image system. The module uses the PHP GD Extension API to provide the system with image operations and manipulation functionality.
The GD toolkit is active on most systems and can be used by the Drupal installation without any additional settings. However site builder may want to add some more advanced graphic toolkits like ImageMagick, provided by contributed modules. If other toolkit is active in the system, "GD Toolkit" can be disabled.