Image SEO
Image SEO is the practice of making images easy for search engines to discover, understand, and display while improving page speed and accessibility.
What I’d do first
- Rename images descriptively before uploading.
- Write alt text for humans first, SEO second.
- Compress and convert to WebP for faster load times.
- Use responsive images to serve the right size for each device.
- Submit an image sitemap if you have hard-to-find images.
The path I'd take
- Audit your existing images. Run a crawl (Screaming Frog, Sitebulb) to find oversized files, missing alt text, and generic filenames.
- Optimize file names and alt text. Batch-rename images with descriptive, hyphenated names. Write alt text that's accurate and concise — aim for 5-15 words.
- Compress and convert. Use lossy compression for photos (80-85% quality is usually fine) and convert to WebP where possible. Keep a JPEG fallback for older browsers.
- Implement responsive images. Add
srcsetandsizesattributes so the browser serves the right size for the viewport. Pair withloading="lazy"for below-the-fold images. - Create an image sitemap. If you have images that aren't easily discoverable (e.g., in JavaScript galleries), submit a dedicated image sitemap via Search Console.
- Add structured data. For key images (product photos, recipe shots), use
ImageObjectschema to give Google explicit context.
Watch-outs
- Don't hide images in CSS backgrounds. Google can't crawl
background-image— use<img>tags for important content. - Avoid lazy loading above the fold. It can delay Largest Contentful Paint (LCP). Only lazy-load images that are off-screen initially.
- Don't block image paths in robots.txt. If you disallow image directories, Google can't index them. Use
noindexmeta tags instead if needed. - Don't use alt text as a keyword dump. Screen readers will read it aloud — make it useful, not spammy.
What I got wrong
I used to upload images at full resolution and let CSS shrink them down. That meant visitors were downloading 5MB files for a 300px thumbnail. Page speed tanked, and my bounce rate climbed. Now I resize images to their display dimensions before uploading — it's the single biggest speed win you can make.
I also used to write alt text like "blue widget for sale" — keyword-stuffed and useless. Now I write "blue widget with ergonomic grip on white background" — descriptive, natural, and actually helpful.
Next step
Quick answers
What is image SEO?
Image SEO is the practice of optimizing images so search engines can discover, understand, and rank them, improving visibility in Google Images and page performance.
How do I write good alt text?
Describe the image accurately and concisely for accessibility; avoid keyword stuffing. Include relevant keywords naturally if they fit the context.
What image format is best for SEO?
WebP is recommended for web use due to superior compression and quality. JPEG and PNG remain acceptable; SVG is best for vector graphics.
Sources
Primary documentation is linked directly. Anything commercial is marked nofollow.
- Google Search Central: Image SEO Best Practices — Primary source for discovery, indexing, responsive images, sitemaps, formats, and image-page optimization.
- Yoast: Image SEO — Widely cited SEO reference with practical guidance on filenames, dimensions, alt text, structured data, and sitemaps.
- Search Engine Journal: Image Optimization Tips — Useful secondary SEO reference covering alt text, compression, responsive images, lazy loading, and crawlability.
Notes from Callum Bennett.