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Why GTmetrix and PageSpeed Still Report Image Issues After Using Smush

16 threads Sep 16, 2025 Plugin → Smush image optimization – optimize images | compress & lazy load images | convert webp & avif | image cdn

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It's a common and frustrating scenario: you've installed the Smush plugin, run the bulk optimizer, and received the 'All images are smushed' confirmation. Yet, when you run a GTmetrix or Google PageSpeed Insights test, you're still greeted with warnings like 'Optimize Images,' 'Serve Scaled Images,' or 'Serve images in next-gen formats.'

This doesn't necessarily mean Smush has failed. These tools report on different types of image optimization, and understanding the distinction is key to resolving these persistent warnings.

Common Reasons for Post-Smush Optimization Warnings

Based on community reports and troubleshooting, here are the most frequent reasons these errors appear even after smushing.

1. The "Serve Scaled Images" Warning

This is one of the most common reports. This warning means the images loaded by your browser are physically larger than the dimensions of the container they are displayed in. For example, your theme might display a product image in a 300x300 pixel box, but the actual image file being served is 1200x1200 pixels.

Why Smush (Free) Doesn't Fix This: The free version of Smush compresses images but does not automatically resize them to fit their HTML containers. This is primarily a theme or development issue.

How to Troubleshoot:

  • Identify the problematic images using the report from GTmetrix/PageSpeed.
  • Check what image size (e.g., 'medium,' 'large,' 'full') your theme is calling for that specific location.
  • Work with your theme developer to ensure the correct, pre-generated WordPress thumbnail size is being used instead of a large image that is scaled down with CSS.
  • The 'Smush Image Optimization' team suggests using a feature in Smush > Tools > Image Resize Detection to help identify these sizing mismatches.

2. The "Optimize Images" Warning on Original/Full-Size Images

You may see a warning that specific images still need lossless compressing. Often, these images are listed as 'full-size' or 'original' images in your uploads directory.

Why Smush (Free) Doesn't Fix This: By default, the free version of Smush is designed to compress all the standard WordPress-generated thumbnail sizes (like thumbnail, medium, large). It explicitly does not compress the original, full-size uploads to preserve image quality for other purposes.

How to Troubleshoot:

  • Check the report to see if the listed images are your original uploads.
  • You can manually optimize these specific images using a third-party tool like Squoosh or ShortPixel before uploading them to WordPress.

3. The "Serve images in next-gen formats" Warning

This warning recommends serving images in modern formats like WebP or AVIF, which offer superior compression compared to older JPEG and PNG formats.

Why Smush (Free) Doesn't Fix This: The ability to convert and serve images in WebP/AVIF formats is not included in the free version of Smush.

How to Troubleshoot:

  • Consider using a dedicated image conversion plugin like WebP Converter for Media or WebP Express.

4. Using an Outdated Testing API

In rare cases, a testing tool might be using an outdated API or cached results.

How to Troubleshoot:

  • Always cross-reference your results. If GTmetrix shows an error, double-check the same URL directly in Google PageSpeed Insights to see if the error persists.

Summary: What Smush Free Can and Cannot Do

To set clear expectations, here is a quick breakdown:

  • Can Do: Excellent lossless and lossy compression of WordPress-generated thumbnails (small, medium, large).
  • Cannot Do: Resize images to fit containers, compress original full-size images, or convert images to next-gen formats like WebP.

Persistent warnings are usually not a bug in Smush but a mismatch between what the plugin is designed to optimize and what the speed test is analyzing. By understanding these distinctions, you can better diagnose the root cause and take the appropriate steps to achieve a higher performance score.

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