Using best practices for creating accessible documents makes Section 508 remediation much less costly. Adding alternative text for images is the imperative, and needs to be done correctly:
- Try to answer the question “what information is the image conveying?”
- If the image does not convey any useful information, leave the alternative text blank (e.g. Background images should generally have no alt text, other decorative images should only have alt text if they form a crucial part of the content, message, and purpose of the document)
- If the image contains meaningful text, ensure all of the text is replicated
- For logos, the alternative text should be the organization name
- For groups of logos, one logo can be chosen to represent the group
- Sometimes text is included as part of a logo or footer image (e.g. the image might contain a phone number), this text should be set as the alternative text of the image
- Alternative text should be fairly short, usually a sentence or less and rarely more than two sentences
- If more description is required (e.g., for a chart or graph), provide a short description in the alternative text (e.g., a summary of the trend) and more detail in the long description, see below
- Test by having others review the document with the images replaced by the alternative text
Tips for writing longer descriptions
- Long descriptions should be used when text alternatives (see above) are insufficient to answer the question “what information is the image conveying?”
- In some situations, the information being conveyed will be how an image looks (e.g., an artwork, architectural detail, etc.). In these cases, try to describe the image without making too many of your own assumptions.
- One approach is to imagine you are describing the image to a person over the phone
- Ensure that you still provide concise alternative text to help readers decide if they are interested in the longer description
Alternatively, you can include the same information conveyed by the image within the body of the document, providing the images as an alternate to the text. In that case, the images should be marked as background and you do not have to provide alternate text within the image.
By following the basic principles outlined here, web developers can make their web content more accessible to individuals with disabilities.
Source: http://adod.idrc.ocad.ca/acrobat9