Empirical Responsive Images – Auto Image Sizes, WebP & AVIF

Activate it and forget it. Empirical Responsive Images finds the images your WordPress site sends too large, then creates the sizes that actually fit. There is nothing to configure, no bulk run to start, no queue to approve, and no account or API key.

Most sites send phones images made for desktops. WordPress can only offer the thumbnail sizes it already has, so when none is close, the browser downloads far more image than the screen can show. PageSpeed Insights reports this as “Improve image delivery” or “Properly size images”, and it can hold back your Largest Contentful Paint (LCP) and Core Web Vitals.

Other tools ask you to guess which image sizes you need. This one measures them on your real pages, so it only creates sizes your layouts use.

What happens after you activate it

None of this needs you. It runs on its own for as long as the plugin is active.

• A small browser check compares each displayed image with the sizes already available. Images with a good match are ignored.
• Missing sizes are confirmed before any work is scheduled.
• WordPress creates the new image files later, as a background task.
• Your existing responsive image markup picks them up, and your cache refreshes.
• Future visitors get a closer image size.

No resizing happens in the visitor’s browser, and no image is generated while a visitor waits for the page.

What you get

• Better-sized responsive images for phones, tablets, laptops, and high-density screens.
• Missing WordPress thumbnails created automatically, so there is no need to regenerate thumbnails for your whole library.
• WebP and AVIF versions when your server supports them.
• Better srcset and sizes choices through normal WordPress markup.
• Coverage for Media Library images and manageable local theme and plugin images.
• Automatic cache refresh after new image files are ready.
• Status tables under Tools > Responsive Images, if you are curious. Nothing there needs your attention.

Your existing custom image choices, crops, and picture layouts stay as they are. The plugin fills proven gaps instead of replacing WordPress responsive images. It is free, and it does not send images to a content delivery network (CDN) or outside image service.

Real result

On one test page, the mobile PageSpeed score went from 75 to 99 and LCP improved from 7.2 seconds to 2.3 seconds. Results depend on your theme, original images, cache, hosting, and other plugins, so no score is guaranteed.

Privacy

Automatic learning reports only what the plugin needs to identify a local image and a rounded missing size. It may also include a general screen size and the space used by the image so WordPress can make a better choice next time.

These reports do not store the page URL, visitor identity, IP address, browser details, or referring page. Reports from logged-out visitors and Subscribers do not send cookies.

An optional detailed view is available only to site administrators. It can store combined image measurements and page paths for troubleshooting. Query strings and raw IP addresses are not saved.

Everything stays on your WordPress site. Nothing is sent to an external service.

Settings, learned size records, and generated images remain after uninstall by default. You can enable full cleanup under Tools > Responsive Images before uninstalling.

Protection against abuse

The plugin accepts work only for images that belong to your site and were marked by the plugin. Visitors cannot submit any image URL or invent unlimited custom sizes.

Normal visitors must confirm the same missing size over time. Hard limits on requests, waiting jobs, retries, image size, daily work, and free disk space keep everything under control. Repeated or invalid reports do not gain priority.

Advanced commands

List learned image sizes:

wp empirical-responsive-images sizes

Generate thumbnails and modern image versions:

wp empirical-responsive-images regenerate --batch-size=10

Force a rebuild:

wp empirical-responsive-images regenerate --force