This is certainly a subject that I’ve covered before — in fact, it’s something I would hardly choose to cover yet again if it didn’t continue cropping up as an important issue. The use of text in alt attributes is an extremely sensitive subject.

Today, the good folks at SEOmoz published an extensive article documenting their statistical findings on web site ranking factors, as gathered from the data in their LinkScape analysis tool. It’s a good article, and demonstrates some interesting results they’ve garnered from the data available in the extensive LinkScape database.

One of their major takeaways in the article was a little disturbing to me.

“Alt attributes of images are probably pretty important places to use your keywords[.]” Explaining (Some of) Google’s Algorithm with Pretty Charts & Math Stuff, October 22nd, 2009

I’m not in anyway disputing their results; their data indicates that placing keywords in alt attributes is of benefit to search engine rankings. Whether that’s true or not is irrelevant to me; I simply want to discuss how this information should be best used.

SEOmoz, of course, is a company dedicated to the study and practice of search engine optimization and marketing. Their goal is to learn what they need to know in order to best put into practice the promotion of web sites. That’s great. My goal, however, is to make sure that users with disabilities are able to use and access web sites successfully without having to jump through unnecessary or unhelpful hoops along their way.

This is a particular case where the SEO method must be used cautiously and selectively if at all. What I want to convey in this article is the fact that while using keywords in alt attributes may help your web site rank, it can also result in a significantly less accessible web site, if applied poorly.

What’s the problem with alt attributes?

While sighted users will never even be aware of an alt attribute value in normal web browsing, screen reader users depend on them. Excess verbiage can render an image-based menu unusable, as I observed in a recent site review at Practical eCommerce. The same unnecessary use of keyword terminology in contextual images can easily confuse or distract a user; and the use of keywords with spacer or ornamental images can cause a web site to be completely unnavigable.

It’s all a question of information overload: practically speaking, if a web site uses images to convey information, a screen reader user can’t disable them without rendering the web site unusable. If the site also fills other images with extra text, the same user may be overwhelmed by an unnecessary volume of keyword phrases.

The SEOmoz report does continue to remark that “Keyword stuffing may be holding you back,” and the overuse of keywords in alt attributes can certainly qualify as keyword stuffing.

You shouldn’t take away from this article that using a keyword in an image alt attribute is totally unacceptable. That’s really not the case: just be selective. I wouldn’t condemn you for using the text “About ProductName” instead of “About” for a navigational image, or using a sensible alt attribute for a contextual image, such as “Woman using our ProductName.” Just remember that keyword stuffing is keyword stuffing, wherever you put the words.

And never place any value in the alt attribute for a purely decorational or spacing image. Please. Just an empty attribute.