You can print images from lots of apps, but many will want to print images based on how large they think they should be and are usually not optimal. Browsers and Preview are among those applications. However opening an image in Quicktime and printing from it will scale images to fill the printed page.
[Editor's note: I have not verified this myself, as my printer is currently awaiting a new ink cartridge!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020215090723539