Good alternative text helps a reader understand what an image contributes here. W3C guidance distinguishes informative, functional, decorative and complex images. A description generated without the surrounding page may miss that purpose even when its visible details are correct.
Give the image a job
Imagine a picture of a blue envelope. On a page about stationery, its colour may matter. Used as a button, its job may be “Send message.” A long description of the folds would not explain that action. This is an editorial example, not a test of any particular model.
Before accepting a draft, finish this sentence: “Without the image, the reader would miss…” If the answer is “nothing beyond decoration,” check whether the image should have an empty alternative instead of a spoken description. An empty alternative is deliberate; omitting the attribute is not the same decision.
Remove guesses and add missing meaning
- Delete unsupported names, emotions and claims about what happened before the picture.
- Keep the information needed for the current page.
- Avoid repeating a nearby caption word for word.
- For a chart, provide the important relationship and accessible data or a longer explanation nearby.
Read the surrounding paragraph together with the proposed alternative. Does the sequence make sense without looking at the picture? Ask that before asking whether the description sounds elegant. The useful draft is the one that serves the reader's task.