On-Page SEO
Image SEO: Alt Text, File Names, Formats and Speed
Images help pages rank in Google Images and make pages more useful. A few practices make the difference.
Google’s image guidance says alt text is the most important attribute for helping it understand an image, that images should sit near relevant text, and that file names give only very light clues.
It also notes images are often the largest contributor to page size, so image SEO and page speed go together.
Short answer: For image SEO, use standard <img> elements (Google doesn’t index CSS background images), write descriptive alt text without keyword stuffing, place images near relevant text with captions where useful, give files descriptive names, use supported formats such as JPEG, PNG, WebP or AVIF, serve responsive sizes with srcset, compress images for speed, and include important images in a sitemap if they’re hard to discover.
Key Takeaways
- Use <img> elements; CSS background images aren’t indexed.
- Alt text is the most important attribute, Google says.
- File names give only very light clues.
- Place images near related text.
- Compress and size images; they’re often the largest part of a page.
Alt text
| Weak | Better |
|---|---|
| alt=”” on an informative image | alt=”Technician repairing a garage door spring” |
| alt=”garage door repair garage door springs best garage door” | alt=”Broken torsion spring on a residential garage door” |
| alt=”IMG_0023″ | alt=”Before and after photo of a cleaned patio” |
Describe what the image shows in context. Decorative images can have empty alt text so screen readers skip them.
Technical checklist
- Use <img src> (with srcset or <picture> for responsive sizes and a src fallback).
- Supported formats: BMP, GIF, JPEG, PNG, WebP, SVG and AVIF; the extension should match the type.
- Descriptive file names such as black-leather-sofa.jpg rather than IMG00023.jpg.
- Consistent image URLs across pages.
- Image sitemap entries for important images Google might not find.
Speed
Serve images at the size they display, compress them, and avoid layout shifts by setting dimensions. Large images are a common cause of slow Largest Contentful Paint; see Core Web Vitals explained.
Product photos
For stores, use clear, high-resolution product images and keep the same image URLs in your feed and structured data. See product page SEO and Merchant Center image issues.
Frequently asked questions
Does alt text help rankings?
It helps Google understand images and helps accessibility. Google calls it the most important image attribute.
Should I rename images before uploading?
Yes, if it’s easy. Descriptive names give light clues; some platforms can’t rename files after upload.
Which image format is best?
Any supported format works. Modern formats like WebP and AVIF are often smaller for the same quality.
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Sources
Last reviewed October 14, 2026.
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