How to do alt text for SEO

Alt text serves two purposes that matter to your clients: accessibility for screen reader users and a ranking signal for image search. From an SEO perspective, Google uses alt text to understand image context, which helps it determine relevance for both regular search results and image search queries. This means poorly optimized alt text is essentially leaving ranking opportunity on the table.

Write alt text that accurately describes what's actually in the image, then naturally incorporate your target keyword if it fits. The mistake most people make is either writing nothing at all or stuffing keywords unnaturally. If you're optimizing a product page and the image shows a "red leather office chair," write exactly that rather than forcing in irrelevant keywords. If your target keyword genuinely belongs there—say, "ergonomic red leather office chair" and that's what appears in the image—include it. The sweet spot is usually 8-12 words, though Google processes longer descriptions fine. Avoid starting with phrases like "image of" or "picture of" since that's redundant; screen readers already announce it's an image.

For your agency clients, this becomes a scalable process. When you're auditing their site, check for images with missing or generic alt text (tools like Screaming Frog flag these immediately). Prioritize high-traffic pages and images that rank for important keywords. Diagram images, charts, and infographics deserve particular attention since they contain information that alt text can actually convey to search engines. For e-commerce sites, each product variant might need slight alt text variations if they're different colors or configurations—don't just copy-paste the same alt text across similar products. Document your alt text strategy in your client deliverables so they understand it's not just "good practice" but an actual ranking factor. When you hand off the site, include clear guidelines so clients or their internal teams maintain this moving forward, otherwise the benefit erodes as new images get added without proper optimization.