Don't use images instead of text links

Search engine optimization is all about text, and if you use images instead of text, even if you have good alt text, search engines will have a harder time ranking your site. This is especially true for navigation. Search engine spiders crawl through your site by following links, and links on images can be more difficult for them to follow or rank than text links. Using images instead of text makes your pages slower for your customers too. You're better off styling your text with CSS, than using images.