Producing Informative Text Alternatives for Images
A picture may be worth a thousand words but what might those words be? How do we go about finding those words? Images are often used to convey information, supplement textual content, and/or add visual appeal to documents. Unless the user can see the image and properly interpret it, the user may not receive the same information. While containers exist for providing text alternatives in various types of electronic documents (including Web pages), they are rarely used. When they are used, the text alternatives are not informative. While guidance currently exists regarding which containers to use in order to provide text alternatives, there is little guidance available regarding what information to include in these containers and how to compose text alternatives. The purpose of this work is to establish a procedure for identifying the information being communicated within an image and provide guidance on how to produce informative text alternatives. Based on related information in the areas of Web accessibility, library cataloguing, captioning and audio description, image retrieval and indexing, art description, and tactile representation, important information communicated by an image were identified and a procedure for producing informative text alternatives using that information was developed. Studies were conducted to determine the effectiveness of the procedure to identify important information about an image. Study 1 determined the information identified about an image when the procedure was not available. It also suggested reasons why people would opt to not provide a text alternative for an image. Study 2 determined the information that people would identify when they were given the procedure and a set of questions to help identify information about an image. Study 3 determined the information people identified when they were required to consider all of the different types of information that may be important in an image. The results from these three studies were compared to determine the effectiveness of the procedure to identify important information about the image. Study 4 presented the information identified in the previous three studies to sighted and visually impaired users to evaluate the importance of such information. This study determined the quality of the information identified in the first three studies and the ability of the procedure to identify important information for a wide set of images. The results of these studies showed that the procedure was effective in identifying a greater amount of important information than without the procedure. Additional guidance was also identified to further help people create informative and useful text alternatives. The studies also showed that the procedure could be applied by different user groups to a wide range of images. The procedure was submitted to the International Standards Organization to become a technical specification, which will be available to people around the world.
text alternatives, images, alt-text
Doctor of Philosophy (Ph.D.)