Image SEO
Optimises images so search engines can discover, understand, and display them while improving page speed, accessibility, and visibility in image search.
If you have ever renamed a file to a keyword and still failed to rank, you already know image SEO is about context, not filenames alone.
Key points
- Write descriptive alt text that describes the image naturally, not a keyword list.
- Use responsive images with srcset and width/height attributes to prevent layout shifts.
- Compress images to modern formats like WebP to reduce file size without losing quality.
- Submit an image sitemap to help Google discover images you might otherwise miss.
- Avoid using CSS backgrounds for important images; use HTML
<img>elements instead. - Original images provide a stronger visual footprint than stock photos for topical relevance.
The travel blog that turned around image search traffic
A travel blog hosted 200 images, each over 2MB, with filenames like IMG_001.jpg. After renaming to 'sunset-bali-beach.webp', resizing to 800px wide, compressing to 80KB, and writing descriptive alt text for each, they also added an image sitemap and structured data. Page load time dropped from 8 seconds to 2.5 seconds, and within three months, traffic from Google Images rose by 40%, adding 15,000 monthly visits.
Three ways image SEO goes wrong
- Generic filenames Using IMG_1234.jpg helps no one. Search engines use filenames as a clue to image content. A descriptive name like 'sunset-bali-beach.webp' provides context, while a generic name offers none, missing an easy signal for relevance.
- Keyword-stuffed alt text Alt text should describe the image for accessibility. Stuffing it with keywords hurts both users and search engine understanding.
- Oversized images Uploading oversized images hurts core web vitals and user experience. Resize to display size, then compress to modern formats.
Four checks before you upload an image
- Descriptive filename Use hyphens between words and describe the image accurately. A filename like 'red-rose-garden.jpg' is far better than 'IMG_001.jpg'.
- Correct dimensions Resize the image to the maximum width it will be displayed. Use width and height attributes to prevent layout shifts.
- Compression Reduce file size without losing quality. Modern formats like WebP can cut size by 30% compared to JPEG while maintaining quality.
- Relevant alt text Write alt text that describes the image as you would to someone who cannot see it. Be concise, accurate, and natural.
Three things image SEO is not
- A ranking guarantee Optimising an image does not guarantee it will rank; seo pictures are only part of the equation. Page context and relevance matter more.
- Only about filenames Infographics seo requires additional structured data and context. Filenames are just one piece of a larger optimisation puzzle.
- A one-time task A single image can be an image seo king if it perfectly answers a query, but standards evolve. New images need optimisation, and old ones may need updates.
Common questions
What are the best image SEO practices?
Use descriptive filenames, alt text, responsive sizes, and compression. Submit an image sitemap and use structured data for important images.
What is the best image size for SEO?
Resize images to the maximum display width. Use width and height attributes to prevent layout shifts. Compress to under 100KB if possible.
What are the best free SEO tools for image optimisation?
Tools like TinyPNG, Squoosh, and ImageOptim compress images for free. WordPress plugins like Smush offer automation.
Sources
- Google Search Central: Image SEO Best Practices Official Google guidelines on image formats, sitemaps, and structured data.
- Yoast: Image SEO Practical advice on filenames, alt text, and compression for WordPress users.
- Search Engine Journal: Image Optimization Tips Covers modern formats, responsive images, and common mistakes.