Image loading issues during A/B testing made us write this article to help the experimenters with the common issue caused by AdBlockers in some A/B testing tools. We found a legit solution for this. Let’s dive a bit deeper to resolve this easily in quick steps.
The Image Loading Problem in A/B Test
What happened: Images in our A/B test worked perfectly on our team’s devices but appeared broken for clients.
The surprise: The issue wasn’t a coding error or corrupted files; it was ad-blockers interfering with the Testing Tool’s CDN.
Why Images Loading Issue in A/B Test Happen
Ad-Blockers Target Testing Platforms
Ad-blocking software automatically blocks domains that contain keywords like:
- “experiments”
- “CDN”
- Other A/B testing indicators
The Testing Tool’s default CDN URLs include these keywords, triggering ad-blockers to block all content, including harmless images. Optimizely mentions the same issue. As sometimes Adblocker causes optimizely tests to fail.
Who Is Affected?
Not affected: Regular users without ad-blockers see images normally
Affected: Users with:
- Browser extensions (uBlock Origin, AdBlock Plus, etc.)
- Privacy-focused browsers with built-in blocking
- Corporate networks with content filtering
The Solution: Use Amazon S3 + CloudFront
Why This Works
CloudFront is neutral infrastructure: Ad-blockers recognize it as a standard content delivery network used across millions of legitimate websites, not an experimentation platform.
No keyword triggers: CloudFront URLs don’t contain experiment-related terms that activate blocking rules.
Universal compatibility: Works for all users regardless of their ad-blocker settings.
Implementation Steps
- Upload images to an S3 bucket (configure for static web hosting)
- Create CloudFront distribution pointing to your S3 bucket
- Generate CloudFront URLs for your images
- Replace Testing Tool CDN URLs with CloudFront URLs in your experiment code
- Test both scenarios with and without ad-blockers enabled
Best Practices for Your Team
During Development
- Host all critical images on neutral CDNs (S3/CloudFront, not Testing Tool CDN)
- Document where each asset is hosted in test specifications
- Use CloudFront for any images essential to the user experience
During Quality Assurance
- Install ad-blockers on at least one testing device
- Test with popular extensions enabled (uBlock Origin, AdBlock Plus)
- Include ad-blocker scenarios in your QA checklist
Know Your Audience
Consider ad-blocker usage rates for your specific audience:
- Higher usage: Developers, tech professionals, privacy-conscious users
- Plan accordingly: If your target demographic values privacy, prioritize neutral hosting from the start
Technical Implementation Steps
For teams looking to implement this solution, here’s the workflow:
- Upload image files to an S3 bucket configured for static web hosting
- Create a CloudFront distribution pointing to your S3 bucket
- Generate CloudFront URLs for your images
- Replace Testing Tool CDN image references with CloudFront URLs in your experiment code
- Verify rendering with and without ad-blockers enabled
This approach ensures that images remain accessible to all users while maintaining fast load times through CloudFront’s global edge network.
How Ad-Blockers See Different CDNs
The Core Issue
Ad-blockers work like security guards with a blacklist. They check every domain you visit against their lists and block anything suspicious.
How Ad-Blockers Make Decisions
Testing Tool CDN = BLOCKED
What ad-blockers see:
- Domain contains words like “experiment,” “test,” “testing tool name”
- Known A/B testing platform
- Primarily used for tracking user behavior
Ad-blocker’s decision: “This looks like tracking software. BLOCK IT.”
Result: Everything hosted there gets blocked—even harmless images
Amazon S3 + CloudFront ✓ ALLOWED
What ad-blockers see:
- Generic infrastructure service
- Used by millions of websites for legitimate purposes
- Hosts everything: product photos, documents, videos, software
Ad-blocker’s decision: “This is essential web infrastructure. Blocking it would break half the internet. ALLOW IT.”
Result: Your images load for everyone
Simple Analogy
Think of it like a security checkpoint:
Testing Tool CDN = A van labeled “Surveillance Equipment Co.”
- Security stops it automatically because of the label
- Doesn’t matter if you’re just delivering cameras for a wedding
CloudFront = A plain delivery truck from Amazon
- Security waves it through
- It’s neutral infrastructure everyone relies on
Why This Matters
Ad-blockers aren’t broken when they block Testing Tool assets. They’re doing exactly what users want: blocking tracking and analytics tools.
The solution isn’t to fight ad-blockers—it’s to host your images somewhere that ad-blockers recognize as neutral infrastructure.
Troubleshooting Checklist
When images appear broken for some users but not others:
✓ Check if affected users have ad-blockers installed
✓ Inspect the image URL. Does it contain experiment-related keywords?
✓ Test the page with common ad-blocker extensions enabled
✓ Migrate images to CloudFront if Testing Tool CDN is causing issues
Key Takeaway
We touched upon this issue in our VWO Testing Issues and How to Troubleshoot Them But we wanted to discuss in detail. As Ad-blockers & AB testing aren’t malfunctioning when they block Testing Tool assets they’re working as designed to protect user privacy.
The solution isn’t to ask users to disable their blockers, but to host images on infrastructure that ad-blockers recognize as neutral and essential for normal web functionality.If you also have similar issues like this Contact Brillmark To get the solution easily as we run multiple experiments everyday and love to resolve common queries like this.
