Alt Text for Images

Alt text is a written description of an image that gets read aloud by screen readers for people who can't see. It's the difference between a blind visitor hearing "image457.jpg" versus hearing "Golden retriever puppy playing in autumn leaves." The key is to describe what matters in context—not just what you see visually, but what the image is there to communicate. Check this: When you add an image, first ask yourself what its job is on the page, then write alt text that fulfills that purpose.

Alt text follows a straightforward decision process based on why an image exists. First, determine the image's purpose: is it conveying information, serving a function like a link or button, or just decorative? This context determines what alt text to write. For informative images like photos or illustrations, write a brief description that conveys the essential meaning. For functional images like icons or linked images, describe what happens when you activate it, not what it looks like. Decorative images get empty alt text (alt="") so screen readers skip them entirely.

The process works differently for different image types. A photo of a product on an e-commerce site needs descriptive alt text like "blue ceramic coffee mug with tree motif" because that information matters to buyers. But that same image used as a decorative background on a blog post would get empty alt text since it doesn't add meaningful content. Context is everything—the same image can need completely different alt text depending on how it's used.

Common mistakes include redundant descriptions like "image of a cat" (screen readers already say "image") or dumping information that belongs in the main text. Alt text should be concise—typically a few words, rarely more than a short sentence. It should never duplicate nearby text content. For complex images like charts or graphs, provide a data table or full description elsewhere on the page, then use brief alt text like "Bar chart showing quarterly revenue" and link to the detailed explanation.

Writing good alt text is a skill that improves with practice. Start by asking: if I removed this image, what information would be lost? If the answer is "nothing important," use empty alt text. If important content would be lost, describe it succinctly. When in doubt, user testing with people who use screen readers provides the clearest feedback on whether your alt text actually works.

Alt text is a foundational requirement of web accessibility standards, enshrined in WCAG 2.1 Success Criterion 1.1.1 (Non-text Content). Research shows that poor alt text remains one of the most pervasive accessibility issues on the web today, despite clear guidelines being available for decades. Studies of screen reader behavior reveal that users rely on alt text not just to understand image content, but to navigate efficiently through pages, decide what to engage with, and determine whether they've found what they're looking for.

• W3C Web Accessibility Initiative (2024): Emphasizes that alt text must be "programmatically determinable" so assistive technologies can extract and present it to users in different modalities, including speech, Braille, and large print [2].
• Henry et al. (2014): Found that screen reader users navigate by headings and links first, then examine images when needed, making accurate functional alt text critical for efficient page exploration [3].

Alt text has inherent constraints that can create accessibility challenges. Extremely complex images like detailed maps, infographics, or works of visual art may require descriptions longer than practical for alt attributes, forcing content creators to decide between oversimplifying or providing separate long-form descriptions. Alt text also struggles with subjective visual elements—humor, emotional impact, aesthetic qualities, and cultural references that depend on visual recognition. Some images serve ambiguous purposes that make the "right" alt text debatable even among accessibility experts. Additionally, alt text cannot convey the experience of seeing an image; it's a functional workaround, not a true equivalent. Emerging AI image description tools show promise but still lack contextual understanding and often produce generic or inaccurate descriptions that require human review.