Images in this tutorial refers specifically to images you'll be adding to your page as part of the design itself or as a means of enhancing the content, such as with photos. Images must be processed in a specific way for the Web, using a good image editor; you can quickly learn the details.
Note: Web graphics can be created by a wide range of programs, but typically you're going to want to have a decent image editor, such as Photoshop (if your wallet is a little smaller, you can try Jasc's Paint Shop Pro). There are numerous other web graphic programs; you can find them by searching for "web graphics software" at your favorite search engine.
Two primary types of web graphic formats exist: GIF and JPEG. The GIF file format is best for images with few, flat colors and line drawings; JPEGs are best for images with many colors and color gradients, such as photos. A third type of web graphic format is PNG, but the lack of support for PNG in some browsers makes it a less stable choice.
Note: Although images, media, and scripting can bring more options to your site, they also can add unnecessary clutter and download time. I like to think of most content of this nature to be decorative. Just as you wouldn't want to over-decorate a house, think about how less can be more when it comes to your page.