Alt Text

Alt text is the text alternative for an image, specified in the HTML <img alt="..."> attribute. It serves three audiences. First, accessibility: screen readers announce alt text to visually impaired users, making images useful rather than silent. Second, search engines: Google reads alt text as a primary signal for understanding what an image depicts and what topic it supports. Third, fallback rendering: when an image fails to load, browsers display the alt text in its place.

Effective alt text describes what the image actually shows in clear, concrete language. For decorative images that carry no informational content (background textures, spacer graphics), the correct value is an empty string (alt="") rather than omitting the attribute entirely — an empty alt tells assistive tech to skip the image, while a missing alt attribute makes screen readers announce the filename, which is almost always worse.

For SEO, alt text doubles as Anchor Text when an image is itself a hyperlink. Linking an image with no alt attribute is the equivalent of linking text-anchored with nothing — search engines cannot infer the link's topical relevance. This is one of the most common on-page misses, particularly on logo-led navigation and image-heavy article layouts.

Practical guidance: write alt text the way you would describe the image to someone over the phone. Include the target keyword naturally if it accurately describes the image. Do not keyword-stuff — alt text reading "best mechanical keyboard cheap online 2025 free shipping" is a textbook over-optimisation pattern. Keep alt text under roughly 125 characters where possible; some screen readers truncate at that length.

For product images on e-commerce sites, include the product name, key attributes (colour, size), and any model number where relevant: "Black mechanical keyboard, 60% layout, Cherry MX Brown switches" rather than "keyboard."

For complex images like charts or diagrams, alt text alone is often insufficient. Provide a longer description either in surrounding body text or via the longdesc attribute (rarely supported now) or aria-describedby pointing to a hidden text block.

Image SEO also depends on file naming (descriptive-keyword.webp beats IMG_8847.JPG), file format and compression (modern formats like WebP and AVIF affect Core Web Vitals), and Schema Markup (ImageObject schema where contextually useful).