The following are common sins of omission or commission by website designers that can cause problems for blind users.
In HTML, the tags used to control images (IMG and AREA) include the ALT attribute, designating alternate text that is supposed to describe the image if it cannot be shown. Originally ALT text was included because the use of graphical displays could not be assumed, but today screen readers rely on ALT text. They pronounce the ALT text with the expectation that it will replace whatever information the image is supposed to convey. (The screen reader cannot "see" the image, and so without the ALT text whatever is in the image is lost.) However, the page designer must provide the ALT text. If none is present the screen reader will usually pronounce the file name, which is rarely meaningful.
"Using ALT tags for your graphics is half the game," says Darren Burton, project manager for technical evaluation with the American Foundation for the Blind out of Huntington, W.V.
Unlabeled Flash animations
Online animations created with Adobe Flash have control buttons that have to be labeled with Flash software rather than HTML -- and this is rarely done, sources agree. Consequently blind users often cannot play Flash animations, although they could typically profit by hearing the audio portion.
"Just being able to press Play would be a big jump forward," says Clara Van Gerven, a National Federation for the Blind technology specialist in Baltimore, indicating that blind users often find value in the audio portion of online videos. The good news, she said, is that "it looks like Flash is on the way out, and HTML5 handles labeling much better."
Inaccessible PDF files
Menus and informational brochures are often posted on the Web in PDF format, but are often just scanned images rather than text. Consequently a screen reader can do little with them. It is possible to add coding to PDF files to make them accessible, but this is rarely done, sources complain.
No heading structure
HTML supplies header tags (H1, H2, etc.) for use in organizing text, and screen readers use the header tags to format the material and facilitate navigation. (Search engines also use header content to assess pages.) But sources complain that, all too often, page designers bypass the official HTML header tags and instead make up their own ad hoc header-like formatting.
"The result is like reading text with all the paragraph markup removed -- a word salad," complains Van Gerven.
A CAPTCHA is a test to ensure that the user is a human being and not a machine before full access to a site is granted. Typically the user is asked to identify distorted letters, effectively excluding blind users.
Sites may offer alternate audio CAPTCHAs, where the listener has to identify spoken letters over background noise. "Ever tried to solve one? The success rate is maybe one in five," says Van Gerven.
The row-and-column Table element in HTML was widely used to control page layouts in the early days of the Web, but today Cascading Style Sheets are a more powerful layout tool. Using Table for that purpose mostly confuses the screen readers, making it difficult for vision-impaired readers to navigate a page built with Table elements rather than Cascading Style Sheets.
Websites can be compliant and still be unusable -- a fact that would come out if sites were actually tested by blind users. A common problem, sources agree, is the use of small graphical files as spacers to control layout. Compliance implies that they should be labeled with the ALT attribute, and often are labeled "Spacer." But there can be scores of them on a page, leaving the screen reader continuously chirping "spacer." In such cases it is better to put in a blank for the name, says Jim Denham, director of assistive technology at the Perkins School for the Blind in Watertown, Mass.
-- Lamont Wood