Accessibility to information for all is right, is important, and is achievable -- Harvey Bingham
A significant opportunity for inclusiveness in website design is to provide redundant information that provides alternative content. This includes text to describe images. This alternative representation helps those who depend upon text-to-speech, or text-to-braille; such as those using phone browsers, or those who cannot see.
Some accessibility problems are common to an entire site, such as any material providing common links that appears on all pages. Identifying any accessibility problems in these and fixing them has high benefit for all.
As an immediate high-payoff enhancement in web pages that are tagged using HTML, make sure that each image includes alt="brief desciption" of the image referenced by the URL. That brief description can be used for pop-overs to explain an image visually (should images be turned off or otherwise undisplayable), also by text-to-speech readers for phone browsers, by assistive technology, such as text-to-braille.
<img href="url" alt="brief description">
At least three tools are available to identify and explain accessibility problems. I suggest accessibility testing your site starting from your entrance URL, as it is likely to be the most commonly used. Then check other pages and apply the same techniques.
This list is provide by the World Wide Web -- Web Accessibility Initiative. The list there has three sub-categories:
Once the accessibility issues with a Web Page or site have been identified, the following identified fifteen tools can assist the author in making the pagers more accessible.
Another eight pages are identified.
I encourage you to also validate the markup and links as well as make those pages accessible.
Xenu's Link Sleuth (tm), by Tilman Hausherr.
Invited Expert, World Wide Web -- Web Accessibility Initiative http://www.w3.org/wai