Good alt text describes the image’s purpose in context rather than every visual detail: a product photo needs alt text describing the product, while a decorative background flourish needs empty alt text (alt=””) so screen readers skip it silently instead of announcing “image” for something that conveys no information. Images that function as links or buttons need alt text describing the destination or action, not the picture itself.
Missing or unhelpful alt text (like alt=”image123.jpg” or a hardcoded empty string on a meaningful image) is consistently one of the single most common accessibility failures found in audits across the web.