Tactics that preclude assistive technology have at their root a search engine optimization method that creates inherent problems; keyword stuffing. Keyword stuffing involves an attempt to gain rankings by forcing as many keywords as possible in a page, utilizing elements such as the title attribute, alt attributes, link titles and more. (Search Engine Guide)

As always, webmasters are free to do what they want on their own sites, but Google reserves the right to do what we think is best to maintain the relevance of our search results, and that includes taking action on keyword stuffing. (mattcutts.com)

Alt tags and image and link title tags are also hot spots for keyword stuffing activity and are another area that search engine spiders crawl (SEO Consult)