search engines can't see images. All they see is the image name and the alt tag if filled. if you use firefox, right click on your site, page info, cached snapshot of page, then text version only in the top right corner. That will basically show you how search engines see your site.
Adding images just for the sake of rankings will not help a bit.
I think people should stop building websites for search engines but actually building websites for people. If you think your website will be improved by adding images, then go ahead.