Definition
Alt text, short for alternative text, is a written description added to the HTML code of an image to explain its content and function. It is displayed when the image cannot be loaded and is read aloud by screen readers for visually impaired users. Alt text is a core accessibility feature that ensures inclusivity in digital content.
In addition to accessibility, alt text supports search engine optimization (SEO) by helping search engines understand the context of images on a webpage. Properly written alt text enhances both usability and discoverability, making it a best practice in web design and digital marketing.
Advanced
Alt text is defined in the HTML alt attribute of the <img> tag. For accessibility compliance, such as WCAG (Web Content Accessibility Guidelines), alt text must be concise yet descriptive, conveying the essential meaning of the image. Decorative images can have empty alt attributes (alt="") to avoid unnecessary noise for screen readers.
Advanced strategies involve using alt text for structured data, e-commerce product listings, and image-heavy platforms where accurate descriptions improve search relevance. Automated tools and AI-based image recognition can assist in generating alt text, but human review is essential for accuracy and context.
Why it matters
- Ensures accessibility for visually impaired users.
- Improves compliance with accessibility regulations like ADA and WCAG.
- Enhances SEO by providing image context to search engines.
- Increases engagement and usability on content-rich websites.
- Reduces bounce rates when images fail to load.
Use cases
- An online store describing product images for visually impaired customers.
- A blog using descriptive alt text to improve search rankings.
- A news site ensuring accessibility compliance with image captions.
- An educational website using alt text for diagrams and charts.
Metrics
- Percentage of images with proper alt text.
- Accessibility audit scores for compliance.
- SEO performance from image search traffic.
- Accuracy and readability of generated alt text.
- User feedback from accessibility testing.
Issues
- Missing alt text reduces accessibility and SEO value.
- Overloaded or keyword-stuffed alt text can harm SEO.
- Inaccurate or vague descriptions confuse users.
- Automated alt text may lack context or meaning.
Example
An e-commerce retailer optimized all product images with descriptive alt text, such as “black leather laptop backpack with padded straps.” This improved accessibility for screen reader users and increased organic traffic from image searches, boosting overall sales.