How exactly are you resaving the files? Screenshots in Panther (10.3) and newer use the PDF format (which is actually just a TIFF or a JPG embedded in a PDF). If you're opening the PDF file in, say, PhotoShop or some graphics-editing program and resaving as a JPG with low quality, that could be where the "fuzziness" you speak of comes into play.
Also, iPhoto as well as Preview uses some image-enhancing technology that works well for the most part, but can make some images appear "blurry" or "fuzzy." This is evident in iPhoto by viewing a photo, and watching as the photo slightly changes about 1/2 second after displaying.