Every site uses small preview-thumbnails with links to the full, large pictures.
But when you link directly to the picture there will be an ugly white border around the image. This way you can customize the way the page around the picture looks like using powerful templates. If you want you can let the script display a description on the picture-page, if not otherwise specified the script will also automatically determine the URL of the page that called the script and place a link back. Get an additional ad-impression per shown picture.