Auditing Your Image Strategy: Tools and Techniques for Web Performance

Beyond PageSpeed Insights

"Your Core Web Vitals look great, but have you audited your image strategy?"

That question usually earns me confused looks from clients who thought running their site through PageSpeed Insights was a comprehensive performance audit. I don't blame them—I used to think the same way.

After conducting image audits for over 50 websites in the past two years, I've realized that while tools like PageSpeed Insights and Lighthouse provide valuable metrics, they're just the beginning. A comprehensive image audit requires deeper analysis to uncover root causes and business impacts that generic tools miss.

Essential Tools for Image Auditing

My audit toolkit has evolved through much trial and error. A client once asked why I needed so many different tools when "Google already has a speed test." After showing them how each tool revealed a different piece of the puzzle, they understood my methodology:

1. WebPageTest: For waterfall analysis and filmstrip views (I love how it visualizes loading sequences)
2. Chrome DevTools: For network, performance, and coverage analysis (my daily companion)
3. Lighthouse CI: For automated performance tracking (caught a regression last week that would have tanked our client's mobile performance)
4. Browser-based Field Data: From CrUX reports and RUM tools (real-world data that often contradicts lab results)
5. Custom Image Analysis Scripts: For image-specific metrics (I built these after getting tired of manually analyzing image data)

Each tool serves a specific purpose in building a complete picture of image performance.

Key Metrics Beyond the Basics

"But our Lighthouse score is 97!" a marketing director once protested when I suggested improving their image strategy. After showing them their 12MB hero image that was loading at 4000px wide on mobile devices, they quickly understood that standard metrics don't tell the whole story.

These image-specific metrics provide much deeper insights:

• Image Weight Ratio: Percentage of page weight from images (I've seen this range from 30% to 82%)
• Efficient Format Usage: Percentage of images using modern formats (one client was still serving PNGs for everything in 2025!)
• Responsive Delivery Accuracy: How well image dimensions match display size (I once found a 4MB product image being displayed at 150×150px)
• Cache Hit Ratio: Percentage of image requests served from cache (this number should be >90% for returning visitors)
• Visual Quality Assessment: Measuring perceptual quality vs. file size (subjective but critical for brand-conscious clients)

Conducting a Thorough Image Audit

Last month, I audited an e-commerce site that "couldn't figure out" why their mobile conversions were half their desktop rate. My systematic approach revealed the answer:

1. Inventory Assessment: Cataloged all image assets (they had 1,200+ product images, all improperly sized)
2. Format Analysis: Checked for obsolete formats (they were using JPEG for transparent product images instead of WebP/PNG)
3. Delivery Evaluation: Assessed how images were requested (found they were loading full-resolution images first, then downsizing)
4. Competitor Benchmarking: Compared against industry leaders (their product pages were 3× larger than competitors)
5. Technical Debt Identification: Flagged systematic issues (their CMS was generating three copies of each image but using none of them)

After implementing our recommendations, their mobile page load went from 8.2s to 2.7s, and conversion rates jumped by 34%.

Sample Audit Checklist

I keep a laminated copy of this checklist in my laptop bag (yes, I'm that person):

□ All images served via CDN
□ Modern formats (WebP/AVIF) delivered to supporting browsers
□ Responsive images implemented with appropriate srcset values
□ Image dimensions appropriate for display size
□ Critical images preloaded
□ Lazy loading implemented for below-fold content
□ Proper cache headers applied
□ Alt text provided for accessibility
□ Art direction implemented for key visuals

This simple checklist has saved countless hours of troubleshooting.

Translating Audit Results into Action

The hardest part of my job isn't finding problems—it's helping teams prioritize solutions. After one particularly overwhelming audit revealed 27 distinct image issues, I developed a framework that helps teams focus:

1. Prioritize by Impact: Focus on high-visibility, high-traffic pages first (fixing the homepage hero image often delivers immediate wins)
2. Quick Wins vs. Strategic Changes: Balance immediate fixes with systemic improvements (updating the CMS settings can prevent future issues)
3. Establish Ongoing Monitoring: Set up automated testing to prevent regression (I've seen perfectly optimized sites degrade over time without monitoring)

In my next post, I'll explore how to implement the ultimate automated image optimization workflow with Skymage—a system I wish I had years ago that would have saved me hundreds of hours of manual optimization.

Ready to receive a professional image audit for your site? Contact Skymage today.