In the category of “stuff it took forever to find, so I’m posting a copy here”:
How to add ALT tags to images in PDFs
You can apply Alt text and ActualText attributes to images to improve the readability of a document being read aloud with screen-reader software for the visually impaired. The Alt text attribute lets you create alternate text that can be read in lieu of viewing a picture. For example, instead of a butterfly image appearing in your PDF file, the text “Butterfly image” appears.
ActualText is similar to Alt text in that it appears in lieu of an image. The ActualText attribute lets you substitute an image that is part of a word, such as when a fancy image is used for a drop cap. In this example, the ActualText attribute allows the drop cap letter to be read as part of the word.
To apply Alt or ActualText attributes to an image:
- To make sure the image is tagged as Figure, select the image, and then click Figure in the Tags palette.
- Choose View > Show Structure to display Structure view.
- Select the Figure image, and then choose New Attribute from the Structure palette menu.
- For Name, type either Alt or ActualText (this feature is case-sensitive).
- For Value, type the text that will appear instead of the image, and then click OK.
When you export to PDF, the Alt text and Actual Text attribute values are stored in the PDF file and can be viewed in the Element Properties window in Adobe Acrobat 5. This alternate text information can then be used when the PDF file is saved from Acrobat as an HTML or XML file. For more information, see your Adobe Acrobat documentation.