Node Gallery uses the imagecache module to generate image derivatives such as thumbnails or smaller display sizes. Imagecache provides the technology to dynamically generate images when the file is accessed for the first time. It offers different actions that it can execute on images, such as resizing or cropping a file to specified dimensions. These actions are grouped into so called "presets". The module uses the file path to determine which preset it should use on an Image.

During the installation of Node Gallery, three such imagecache presets are generated, corresponding to different contexts:

- node-gallery-thumbnail: A preset that will be applied to thumbnails, e.g. displayed on gallery summaries and teasers.
- node-gallery-cover: A preset that will be applied when only the cover image is displayed for a gallery.
- node-gallery-display: A preset that will be applied to images as they appear on their full node page.
- node-gallery-admin-thumbnail: A preset creating a micro thumbnail to display images on administrative pages, such as the manage images and sort images screens.

The imagecache presets can be freely customized to suit your requirements. To learn how to use imagecache and how to customize those presets, please refer to the Imagecache documentation on drupal.org.