Image SEO is the practice of optimising images so they rank in Google Image Search, load faster, and contribute to overall page rankings. In 2025, with visual search growing and Google using images as page quality signals, image SEO is no longer optional — it's essential.
This guide covers every aspect of image SEO from file naming to structured data.
Before uploading any image, rename it descriptively. Use hyphens between words.
| Bad filename | Good filename |
|---|---|
| IMG_20230415_123456.jpg | handmade-silver-ring-turquoise-stone.jpg |
| photo1.jpeg | chocolate-fudge-cake-recipe.jpg |
| DSC00234.png | eiffel-tower-paris-sunset.png |
Alt text is the single most important image SEO factor. Every image must have a unique, descriptive alt tag under 125 characters. Read our full alt text guide for detailed instructions and 15 examples.
| Format | Best For | Typical Size |
|---|---|---|
| JPEG/JPG | Photos, complex images with many colours | 50–200KB |
| PNG | Images needing transparency, logos, screenshots | 50–500KB |
| WebP | Best overall — smaller than JPEG at same quality | 30–120KB |
| SVG | Icons, logos, simple illustrations | 1–50KB |
| AVIF | Next-gen, best compression — not universal browser support yet | 20–80KB |
Large images are the most common cause of slow page load times. Target these file sizes:
Free compression tools: TinyPNG, Squoosh (squoosh.app), ImageOptim (Mac).
Always specify width and height attributes on your img tags. This prevents layout shift — a Core Web Vital measured by Google:
<img src="cake.jpg" alt="Chocolate cake" width="800" height="600">
Use the srcset attribute to serve different sizes to different screen sizes, avoiding mobile users downloading desktop-sized images.
Captions are the text directly below images. Studies consistently show captions are read 300% more often than body text. They also provide additional keyword context for search engines. Not every image needs a caption, but important editorial images benefit greatly.
If your site is image-heavy (photography, stock, e-commerce), create a dedicated image sitemap or include image data in your main sitemap. This helps Google discover and index images that it might otherwise miss.
Adding schema markup to pages with images helps Google understand the context. For recipes, add ImageObject schema. For products, include product images in Product schema. For articles, include a featured image in Article schema.
| Task | Priority | Impact |
|---|---|---|
| Descriptive file names | High | Medium |
| Alt text on every image | Critical | High |
| Compress all images | High | High (page speed) |
| Use WebP format | Medium | Medium |
| Specify width/height | Medium | Medium (CLS) |
| Add captions where relevant | Low | Low-Medium |
| Submit image sitemap | Medium | Medium |
| Add structured data | Low | Low-Medium |
For an existing site adding alt text to existing images: expect to see changes in Google Search Console within 2-4 weeks as Google recrawls pages. For image search rankings: 4-12 weeks typically. New sites take longer as domain authority builds.
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