Alt Text
Alt text (alternative text) is a short text description that you assign to an image in the HTML code. It explains in words what can be seen in the image. Screen readers read it aloud to blind people, and search engines and AI systems use it to understand the image content. If an image cannot be loaded, the alt text appears in its place.
Why alt text matters for AI visibility
AI systems and search engines do not see an image the way you do. They read the surrounding code. The alt text is often the most important text source for classifying the image content. If it is missing, the image remains a blind spot for machines. If a precise description is there, an AI assistant can understand the image, categorize it thematically and, if in doubt, draw on your page as a source. For AI visibility this means: good alt texts are what make visual content machine-readable in the first place. Especially with product photos, infographics or diagrams, the image carries core information that appears nowhere else in the text. Without alt text this information is lost for generative search.
How alt text works technically
In the HTML code, the alt text sits in the so-called alt attribute of an image element, i.e. something like alt="description of the image". The attribute is part of the web standard and is evaluated by every browser, every screen reader and every crawler. A crawler is a program that automatically searches web pages. You write the text so that it factually summarizes the image content in one or two sentences. Context is important: a photo of a coffee cup on a cafe page needs a different description than the same photo in an article about porcelain manufacturing. Purely decorative images that carry no information get an empty alt attribute, so that screen readers skip them and don't bother users with irrelevancies.
Common mistakes
The classic mistake is the missing alt text, followed by empty phrases like "image" or the bare file name like "IMG_4823.jpg". Neither helps people nor machines. Equally widespread is stuffing it with search terms, so-called keyword stuffing. This looks manipulative and can harm you rather than help. Another mistake: descriptions that ignore the context or are far too long. An alt text is not an image title and not a caption. It should describe briefly, not advertise. The words "image of" at the beginning are also superfluous, because screen readers announce that an image follows anyway. When in doubt, check: would the description help someone who cannot see the image?
Relevance to AI recommendations
When an AI assistant like ChatGPT or Perplexity makes a recommendation, it relies on the text signals of your page. Alt texts are part of that. They help the system grasp the connection between image and topic and increase the chance that your content is understood correctly and cited. Multimodal AI that analyzes images directly additionally uses the alt text as a check on its own interpretation. For you as an operator this means: alt texts are a small, often underestimated lever. They do not replace a good content strategy, but they close a gap that many competitors leave open. Anyone who cleanly describes visual content gives search engines and AI systems more clues to make their own brand visible.
Example
An online shop for bicycles shows a photo of a red city bike with a basket. Poor alt text: "bike-new-2024.jpg". Better alt text: "Red city bike with a woven wicker basket and coaster brake, side view". This description tells both human and machine exactly what can be seen. If someone searches for a city bike with a basket, the search engine can categorize the image. If someone asks an AI assistant for suitable everyday bikes, the system understands the product context and is more likely to name the shop as a source. The effort: one sentence per image.
Common questions
How long should an alt text be?
As a rule, one or two short sentences, usually under 125 characters. Describe the essentials precisely. Too short says nothing, too long loses the core and is read out clumsily by screen readers.
Do all images really need an alt text?
All informative images, yes. Purely decorative images that carry no content information get an empty alt attribute. That way screen readers skip them and don't bother users with irrelevancies.