Accessible diagram copy should communicate the information needed for the same task, while the visible caption provides context, source, and interpretation boundaries for every reader.
Write for the purpose of the image
State what the diagram helps the audience understand in its surrounding context. Describe the essential parts, relationships, direction, comparison, or trend needed for that task. Avoid listing every decorative element or repeating nearby text. When the diagram contains substantial data or a complex process, provide a longer text description or structured table near the image so the same information is available without relying on a single long alt attribute.
W3C's image tutorials route alt-text choices through the image's purpose, including whether it is informative, decorative, functional, text-bearing, complex, or part of a group. That decision should happen before export. A visual that serves as a link or control needs a functional name, while a decorative asset can use an empty alternative. A technical mechanism usually needs an informative alternative and nearby extended explanation.
Let the caption carry context and provenance
The visible caption should identify the mechanism, population or system boundary, time or version, and the main takeaway supported by the figure. Add the source and explain any adaptation, normalization, or interpretation material to understanding it. Keep uncertainty and excluded conditions visible. For video, captions should follow the final narration and align with the visual beat they describe.
Reality Contact, LLC supplies captions, alt text, and evidence notes with Source-Led Explainer, but the buyer approves accessibility and publication requirements. The service can prepare meaningful alternatives for the agreed artifact. It does not certify conformance across the buyer's site, player, presentation software, document format, assistive technologies, languages, or distribution channels.
Where the service stops
Reality Contact, LLC translates approved material into diagrams and a short explainer, but does not conduct new research, validate scientific truth, approve claims, alter data, provide legal or medical advice, or promise comprehension, persuasion, publication, or audience response. The buyer approves the source corpus, claim boundary, visual brief, diagram drafts, storyboard, narration, and final captures, then decides where and how the finished materials are published or presented. This is visual communication and document preparation, and it does not replace scientific, legal, medical, accessibility, licensing, or professional review. The buyer approves the source corpus, claims, permissions, visual interpretation, narration, and every publication or presentation use.
Sources: W3C Web Accessibility Initiative image tutorials; W3C guidance for accessible audio and video.