GIF images use 8 bits of color information per pixel for a total of 256 colors. Since many photographs require more colors than this, additional colors are provided via dithering. Dithered colors are created by mixing pixels of different colors together to create the illusion of a color that is not one of the 256 available colors. GIF images can be interlaced, meaning they download in stages and they can have a transparent color meaning that the background will show through. Another very neat feature of GIF files is that they support animation and it is fun to include animated GIF files on your website.
JPEG images use 24 bits of information per pixel for a total of 16,777,216 colors. Hence, the JPEG format is particularly suited for photographs which often contain more than 256 colors. JPEG files may also be downloaded in stages if they are saved as progressive JPEG files.
The PNG format was created as a possible replacement for GIF files and they share many of the same features. The PNG format does not support animation.
An image may be divided into regions called hotzones. Each hotzone is hyperlinked to a different web page. Hotzones are easy to create in Microsoft FrontPage using the picture toolbar.
Image processing software allows you to apply filters, adjust brightness and contrast add professional looking borders, crop, resize and make numerous other adjustments to an image.