Images make a page engaging, but they are also frequently the heaviest part of it and a missed SEO opportunity. Image SEO is the practice of optimizing your images so they load fast, are accessible, and can rank in Google Images — driving an extra channel of traffic while improving the experience of your main pages.

Why image optimization matters

There are two big payoffs. First, performance: unoptimized images bloat page weight, slow your Largest Contentful Paint, and hurt Core Web Vitals. Second, discoverability: well-optimized images can rank in Google Images and image packs, bringing visitors who might never have found your page through a text search. Accessibility is a third benefit — descriptive images help users who rely on screen readers.

The image SEO checklist

  • Use modern formats. WebP and AVIF deliver the same quality at a fraction of the file size of JPEG or PNG.
  • Compress every image. Reduce file size without visible quality loss before uploading.
  • Size images correctly. Serve images at the dimensions they display — do not load a huge file and shrink it in the browser.
  • Set width and height. Explicit dimensions prevent layout shift (CLS).
  • Lazy-load below the fold. Defer offscreen images so the initial view loads faster.
  • Write descriptive ALT text. Describe the image naturally, including the keyword where relevant.
  • Use meaningful file names. 'blue-running-shoes.jpg' beats 'IMG_4821.jpg'.

ALT text done right

ALT text is both an accessibility feature and a ranking signal for image search. Describe what the image actually shows in a natural sentence, and include your target keyword only where it genuinely fits — never stuff keywords. Decorative images that add no information can use empty ALT text so screen readers skip them. Find images missing ALT text across a page with the Image ALT Text Checker.

Images and page speed

Because images dominate page weight, optimizing them is often the single biggest speed win. Measure your page's total weight and load time with the Page Speed & Size Test, and confirm your server compresses assets with the Gzip / Brotli Compression Test. Pairing image optimization with these checks can dramatically improve your Core Web Vitals — see our Core Web Vitals guide.

Frequently asked questions

Should every image have ALT text?

Every meaningful image should, for both accessibility and image SEO. Purely decorative images that convey no information can use empty ALT text (alt="") so assistive technology skips them rather than reading a useless description.

What is the best image format for SEO?

WebP is the current sweet spot — broadly supported and much smaller than JPEG or PNG at the same quality. AVIF is even more efficient where supported. The best format is whichever delivers acceptable quality at the smallest file size for your audience.

Conclusion

Image SEO is a two-for-one win: faster pages and an extra traffic channel from image search. Use modern compressed formats, size images correctly, set dimensions, lazy-load, and write descriptive ALT text and file names. Check your images with the Image ALT Text Checker and your speed with the Page Speed & Size Test, and fold it into your overall on-page SEO.

A practical workflow is to build image optimization into your publishing process rather than treating it as a clean-up task. Compress and convert images to a modern format before you upload them, write the ALT text and file name as you add each image, and set dimensions in your template by default. When optimization happens automatically at the point of creation, your pages stay fast and accessible without anyone having to remember a checklist — and the cumulative effect across hundreds of images is enormous.