Thumbnail view shows preview pictures for various file types. The size of the preview pictures can be configured via
Configuration - Thumbnails, as well as several other options. In addition to the thumbnail and the file name, you can display user-defined fields like the file size, or (via a plugin) digital camera information like exposure time.
Thumbnails currently work in normal file mode, but not with archives or ftp connections. Some file system plugins may also support thumbnails now. In virtual folders, thumbnails cannot be loaded from Lister plugins.