Image SEO: optimize images for search
Images affect search rankings in two ways: directly through image search and accessibility signals, and indirectly through page speed and Core Web Vitals. This guide covers both, with the highest-impact fixes first.
How images influence SEO
Search engines reward fast pages, and images are the most common cause of slow ones. Heavy images hurt Largest Contentful Paint and Cumulative Layout Shift — two Core Web Vitals that feed Google’s page-experience signals. Separately, descriptive alt text and file names help images rank in image search and improve accessibility.
The image SEO checklist, in priority order
- 1
Cut image weight
Resize to display size and convert to WebP/AVIF. This improves LCP, the single most impactful image-SEO factor.
- 2
Set width and height
Declare dimensions on every image so the browser reserves space and avoids layout shift (CLS).
- 3
Write descriptive alt text
Describe the image accurately for screen readers and image search. Avoid keyword stuffing; describe what’s actually shown.
- 4
Use descriptive file names
blue-running-shoe.webp beats IMG_4821.jpg for both users and image search.
- 5
Lazy-load below the fold
Defer offscreen images so they don’t compete with the LCP image for bandwidth.
- 6
Prioritize the LCP image
Load the hero/LCP image eagerly with high priority; never lazy-load it.
Audit before you optimize
You can’t fix what you can’t see. Optimagio’s free website image audit scans a page for oversized images, missing modern formats, the likely LCP candidate, missing dimensions, and alt/accessibility gaps — turning this checklist into a concrete, ranked to-do list for any URL.
Frequently asked questions
Do images affect SEO?
Yes, in two ways. Image weight affects page speed and Core Web Vitals (especially LCP and CLS), which feed Google’s page-experience signals. And descriptive alt text and file names help images rank in image search and improve accessibility.
What is the most important image SEO factor?
Reducing image file size — by resizing to display dimensions and converting to WebP/AVIF — because it improves Largest Contentful Paint, the most impactful image-related Core Web Vital.
How should I write image alt text for SEO?
Describe the image accurately and concisely as if to someone who can’t see it. Include relevant context, but don’t stuff keywords — accuracy serves both accessibility and image search.
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