How to Optimize Images for SEO: A Complete Checklist

Why Image SEO Matters

Google Images drives significant traffic for many websites — and images also affect page speed, which is a direct ranking factor. Properly optimized images can:

• Rank in Google Image search and drive traffic
• Improve Core Web Vitals scores (LCP especially)
• Reduce bounce rate by making pages load faster
• Contribute to topical relevance signals for the page

Here's the complete checklist.

✅ 1. Use Descriptive File Names

Rename your images before uploading. Google reads file names as a relevance signal.

Bad	Good
IMG_4821.jpg	blue-running-shoes-nike.jpg
photo1.png	how-to-compress-pdf-screenshot.png
untitled.webp	london-bridge-sunset.webp

Use hyphens between words, not underscores. Keep names concise and descriptive.

✅ 2. Write Useful Alt Text

Alt text serves two purposes: accessibility (screen readers) and SEO (Google uses it to understand image content).

Rules for alt text:

• Describe what's actually in the image
• Include your target keyword naturally where it fits
• Keep it under 125 characters
• Don't stuff keywords — write for humans first

Bad alt text	Good alt text
image1	Screenshot of the PDF compression tool showing a 68% file size reduction
pdf	A PDF document being compressed from 4.2MB to 1.3MB

✅ 3. Compress Every Image

Page speed is a confirmed ranking factor. Large images slow down your page and hurt your Core Web Vitals score (specifically LCP — Largest Contentful Paint).

Target file sizes:

• Hero image: under 300KB
• Blog images: under 150KB
• Thumbnails: under 30KB

Compress images free →

✅ 4. Use the Right Image Format

WebP is now the recommended format for web images. It's 25–35% smaller than JPG at equivalent quality and is supported by all modern browsers.

Convert images to WebP →

For images with transparency, use WebP (with transparency) instead of PNG where possible.

✅ 5. Resize Images to Display Dimensions

Don't upload a 4000px wide image if it's displayed at 800px. Resize before uploading — this alone reduces file size by 70%+ in many cases.

Resize images free →

✅ 6. Use Responsive Images in HTML

Use the srcset attribute to serve different image sizes to different screen sizes:

<img
  src="image-800w.webp"
  srcset="image-400w.webp 400w, image-800w.webp 800w, image-1200w.webp 1200w"
  sizes="(max-width: 600px) 400px, (max-width: 1000px) 800px, 1200px"
  alt="Descriptive alt text"
  loading="lazy"
/>

✅ 7. Add Loading="lazy" for Below-Fold Images

This tells the browser not to load images until the user scrolls near them, improving initial page load time.

<img src="example.webp" alt="Description" loading="lazy" />

Don't add lazy loading to above-the-fold images — they should load immediately.

✅ 8. Add Image Structured Data (for Key Images)

For product images and article featured images, add structured data to help Google display rich results.

{
  "@context": "https://schema.org",
  "@type": "ImageObject",
  "url": "https://example.com/image.webp",
  "width": 1200,
  "height": 630,
  "caption": "Image description"
}

The Quick Wins

If you do nothing else, do these three things — they'll cover 80% of the SEO and performance benefit:

1. Rename files with descriptive, keyword-relevant names
2. Write meaningful alt text for every image
3. Compress and convert to WebP before uploading

Start optimizing your images →