On many web pages and in PDF files images are presented in a minimal size to give
the viewer some idea of whether or not they want to download the full image or not.
These smaller copies of the images are called "thumbnail images" and using them
allows the viewer to see a dozen or more thumbnails on the same screen making it
easy to organize images. There is no standard thumbnail format. The term "thumbnails"
simply refers to smaller views of images that are easier to locate and organize. For
instance, thumbnails on web pages are just smaller gifs or jpgs of the original image.
Graphic Workshop creates its own .thn format files. Graphic Converter creates
standard Mac icons for the image file which are smaller versions of the image.