Specifies that the thumbnail for an image will be loaded instead of the full image. A thumbnail is often available for images returned by digital cameras (EXIF Thumbnail). It applies to JPEG, RAW, IEN, PSD files, and also images loaded using TIEWICReader.
If enabled, and the file does not contain a thumbnail then the next best option will be used instead (e.g. loading an embedded preview image or failing that, the full image).