When people think of search engines, Google, Yahoo, and Bing always come to mind first. However, YouTube is the second ranked search engine on the web, ahead of both Yahoo! and Bing. The point is, images and video are everywhere on the web and it is important to be optimized for both.
While search engine spiders cannot read the content of video and images, they can be optimized in a way that is effective. It is important to communicate as much information as you can to the search engines about each graphic or media piece that you use on your site.