Not everybody views the Web the same way. In fact, lots of people don't "view" the Web at all, but they spend as much time online as anyone else. It's just that they're listening rather than reading or watching.
Using the alt attribute of HTML image tags to add a text description of a picture is second nature to anyone who posts many images or other graphics online. It's almost as easy to provide alternative text for graphics in Microsoft Word and other Office applications. Making sure the alternative text persists when Office files are converted to PDFs requires a couple of extra steps. Adding the text descriptions to images and figures in PDFs is even trickier.
The details on entering alternative text in the 2007 versions of Word, Excel, Outlook, and PowerPoint are on Microsoft's Help and How-to site. In a nutshell, right-click the object and select Size (Word and Outlook), Size and Properties (Excel), or Size and Position (PowerPoint). Click the Alt text tab and enter a short description of the picture or other graphic. (You needn't include "picture of" or "image of" because that will likely be evident from the screen-reader program, nor should you repeat a caption, which also is recited by the screen reader.)
The process is similar in Word 2003, but after right-clicking the graphic, select Format Picture and then the Web tab to find the Alternative text box. Instructions for doing so in other Office 2003 apps are available by entering "alternative text" and the product's name in the search box at the Microsoft Office Help and How-to site.
Preserve alternative text when converting files to PDFs
There's a twist to bringing the alternative text along when creating PDFs out of a Word doc or other Office file. If you choose Print > Adobe PDF, the alternative text is left behind. Instead, click the Adobe PDF menu option in the Office app and choose Change Conversion Settings. On the Settings tab, make sure Enable Accessibility and Reflow With Tagged PDF is selected. You may also want to choose Convert Document Information, Add Bookmarks, and Add Links.
Next, click the Security tab and select Enable Text Access for Screen Reader Devices for the Visually Impaired (this setting should be on by default). If you add bookmarks, click the Bookmarks tab and select a style. Once you've made your choices, click OK and then select Convert to Adobe PDF. Finally, name the file and choose a location to store it. Adobe provides a ton of detail on the subject in the PDF (of course) Creating Accessible Adobe PDF Files.
Add alternative text to graphics in PDFs
If you're working on a Word doc that will be converted to a screen reader-friendly PDF, it's easier to add the alternative text in Word and take the extra steps when converting it to PDF than to enter the image-describing text in Acrobat. Adobe's Using Acrobat 9 Pro site includes an article describing how to add alternative text to links, graphics, and abbreviated terms in PDFs. Another article on the Adobe help site explains how to use Acrobat's Accessibility Full Check option.
In my limited experience, it was cumbersome to use Acrobat 9 Pro's Full Check and the TouchUp Reordering Tool to add alternative text to figures in a PDF. All individual elements are numbered, which clutters the screen of complicated formats. Once you find the figure in need of alternative text, right-click it and choose Edit Alternative Text. You enter the description on the image itself rather than in a pop-up window.
There's much more to Section 508 compliance than alternative text. The U.S. Department of Health & Human Services site provides a five-module online course on testing documents for Section 508 compliance. But accessibility isn't just for the government. With a small amount of effort, you can improve your document's reception for people who "read" with their ears.