Print images need to be created at 300 dpi or there will be a substantial drop in the image quality.

File formats like gif or jpg compress the pictures color and pixel resolution and this can cause color shifts and blurriness. Since jpg and gif are the most predominant image formats on the web, it's not a good idea to simply lift an image from someone's website and use it in your layout they are probably only 72dpi in resolution and will look very blurry if printed on a printing press. Doing so will result in undesirable image quality.

You should scan your images using a resolution of 300dpi at the final dimensions you intend to use them so that your colors will look smooth, and hard objects will look sharp. In other words don't scan at 300dpi and then enlarge the picture by 200% in your layout program!

If you are using pictures from your digital camera they will work just fine if they are jpgs; the quality of jpg images from digital cameras seems to be much better than jpgs that are used on the web. You must do the math to make sure that it is high enough in pixel resolution though. For instance, if your camera puts out a typical image of 1280 x 960 pixels at 72dpi you get about 17" x 13" of photograph (at 72 dpi); this is the same amount of detail as an image which is 4" x 3" at 300 dpi that is ready to print so plan accordingly.