Tim Berners-Lee may have said
"The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect."
Which sounds like a pretty basic right.
There is technology available to read the words on a web page out loud for people with impaired vision, but what about the pictures, YOUR pictures?
The alt attribute in HTML can be used to help provide a written description associated with an image. This is a great help. With the picture having an associated text, that too can be read aloud.
There are other advantages with technology being able to access the text associated with a picture - search engines can now have and idea about the image. The search engine can index the text on the site but without alt attributes it is blind to the pictures.
Some sites are picture rich and lacking words, associating text to these photos is imperative to give search engines, text only viewers and the visually impaired a chance to access all the information on the site (YOUR site).
Adding alt text to your images is a win win move. You win with better search engine indexed pages and your visitors can win by having greater choice in how they 'view' your page. With more visitors being able to access your site, the more visitors get to hear your message, share your hobbies, buy your product.
If you would like to see HOW to add the alt attribute and some associated text or alt text or even alt="text" to the HTML within the webs site builder then have a look at alt attribute - the link opens in a new window.
If you wanted to try a free web browser for blind people with little or no sight, try webbie you may find it useful to show where your site needs a bit of help to make it more accessible to people and machines!
From what I can see, its only for those with a version of windows, but that covers a big chunk of my visitors.