What's in an ALT Tag? Exploring Caption Content Priorities through Collaborative Captioning

Evaluating the quality of accessible image captions with human raters is difficult, as it may be difficult for a visually impaired user to know how comprehensive a caption is, whereas a sighted assistant may not know what information a user will need from a caption. To explore how image captioners and caption consumers assess caption content, we conducted a series of collaborative captioning sessions in which six pairs, consisting of a blind person and their sighted partner, worked together to discuss, create, and evaluate image captions. By making captioning a collaborative task, we were able to observe captioning strategies, to elicit questions and answers about image captions, and to explore blind users’ caption preferences. Our findings provide insight about the process of creating good captions and serve as a case study for cross-ability collaboration between blind and sighted people.