Optimizing Images for Web: Best Practices for 2024

Images typically account for 50-80% of a webpage's total size. Optimizing these assets is one of the most effective ways to improve site performance, enhance user experience, and boost SEO rankings. This guide covers the essential best practices for web image optimization in 2024.

Why Image Optimization Matters

Properly optimized images deliver multiple benefits:

• Faster page loads: Reduces bounce rates and increases engagement
• Improved SEO: Page speed is a ranking factor for search engines
• Lower bandwidth costs: Especially important for high-traffic sites
• Better user experience: Particularly on mobile devices and slower connections
• Reduced carbon footprint: More efficient websites consume less energy

Key Optimization Strategies

1. Choose the Right Format

Different image types call for different formats:

• Photos and complex images with many colors: AVIF (with JPG fallback)
• Graphics, logos, and illustrations: SVG (when possible) or PNG
• Screenshots with text: PNG or lossless WebP
• Animations: WebP or AVIF instead of GIF

2. Implement Responsive Images

Using responsive images ensures users download only what they need:

<picture>
  <source srcset="image-large.avif" media="(min-width: 1200px)" type="image/avif">
  <source srcset="image-large.webp" media="(min-width: 1200px)" type="image/webp">
  <source srcset="image-medium.avif" media="(min-width: 800px)" type="image/avif">
  <source srcset="image-medium.webp" media="(min-width: 800px)" type="image/webp">
  <source srcset="image-small.avif" type="image/avif">
  <source srcset="image-small.webp" type="image/webp">
  <img src="image-small.jpg" alt="Descriptive alt text" loading="lazy">
</picture>

3. Optimize Quality Settings

Finding the optimal quality balance:

• For JPEG/JPG: Quality 70-80% is usually sufficient for web use
• For AVIF: Quality 50-60% often provides excellent results
• For WebP: Quality 75% typically offers a good balance

4. Implement Lazy Loading

Modern browsers support native lazy loading:

<img src="image.jpg" alt="Description" loading="lazy">

For older browsers, consider using an Intersection Observer-based solution.

5. Serve Next-Gen Formats with Fallbacks

Modern image formats can reduce file size by 25-50%, but require fallbacks:

<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Description">
</picture>

6. Use Image CDNs

Consider using an image CDN that can:

• Automatically serve optimized formats
• Resize images based on device
• Apply compression on-the-fly
• Cache images at edge locations

7. Optimize for Core Web Vitals

Pay special attention to:

• Largest Contentful Paint (LCP): Optimize above-the-fold images
• Cumulative Layout Shift (CLS): Always specify image dimensions
• First Input Delay (FID): Ensure image loading doesn't block interactivity

Tools for Image Optimization

Online Tools and Services

• Our AVIF to JPG converter for legacy compatibility
• TinyPNG for PNG optimization
• Squoosh for browser-based optimization
• SVGOMG for SVG optimization

Build Process Integration

• sharp (Node.js)
• Imagemin (with various plugins)
• Next.js Image component
• Gatsby Image plugin

Measuring the Impact

Always measure the impact of your optimizations:

1. Use Lighthouse or PageSpeed Insights to assess overall performance
2. Monitor Core Web Vitals in Google Search Console
3. Compare before/after metrics in your analytics platform
4. Test on various devices and connection types

Advanced Techniques

For those looking to push performance further:

• LQIP (Low Quality Image Placeholders): Show a tiny blurred image while the full image loads
• Art direction: Serve completely different images based on screen size
• Image compression API: Build image optimization directly into your backend
• Preloading critical images: Use <link rel="preload"> for important above-the-fold images

Conclusion

Image optimization is not a one-time task but an ongoing process. As new formats emerge and browser support evolves, regularly revisiting your image strategy ensures your site maintains optimal performance.

By implementing these best practices, you can significantly improve your website's loading times, user experience, and search engine rankings—all while potentially reducing your hosting costs and environmental impact.