Some people use text-based browsers. And some people turn off the automatic image-loading on their graphical browsers in order to speed up download times. What does your page look like if the images don't load?

Image Intensive Pages

These take forever to load. Have pity on the poor person with the slow modem half the world away and keep the images to a minimum. At the very least, warn your visitors that they are about to download many kilo- or mega-bytes of images.

Image Maps

Image maps should be your last refuge. If there is an alternative to an image map, use it!

Images Used for Navigation

Always use text-based links for navigation for the reasons given above.

Animated Images

They used to look very clever but flittering, bouncing, blinking images tend to distract the eye and fool the browser into thinking it has not completed loading the page. If the purpose of the page is to show off the animated image, fine. Otherwise, they are best avoided.