Also, use the alt= parameter to create some text which will appear in place of the image.
Make sure there are text versions of all links. Many searchers have "turned off" images in their browser. In addition, text loads faster than images so that visitors can circumvent a Network bottleneck by clicking on a text link even before the images load.
Finally, you can speed the loading of other pages by including trailing slashes for directories in the urls for your links. This saves a server GET request.