Images, audio and video should all have text alternatives available in the form of alt text descriptions, closed captions and transcripts. This makes the content accessible to users with visual or hearing impairments. It also provides more information to search engines, which rely on text to find out about a site.
In a past piece on the SEO benefits of web accessibility, Mark Jackson explained that text browsers, which ignore graphic content, are often used to review how a website appears to a search engine. A website will appear in the same way to users of a screen reader, which can interpret the web for those who are blind, visually impaired, illiterate or learning disabled. In other words, making the text-based ‘version’ of your website as comprehensive as possible has benefits for both accessibility and search.
from Delicious http://ift.tt/1p7Z0L4