Title: Empirical Responsive Images
Author: Jesus Iniesta
Published: July 28, 2026
Last modified: July 28, 2026
---
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# Empirical Responsive Images
By [Jesus Iniesta](https://profiles.wordpress.org/jesusinica/)
[Download](https://downloads.wordpress.org/plugin/empirical-responsive-images.0.2.0.zip)
* [Details](https://wordpress.org/plugins/empirical-responsive-images/#description)
* [Reviews](https://wordpress.org/plugins/empirical-responsive-images/#reviews)
* [Installation](https://wordpress.org/plugins/empirical-responsive-images/#installation)
* [Development](https://wordpress.org/plugins/empirical-responsive-images/#developers)
[Support](https://wordpress.org/support/plugin/empirical-responsive-images/)
## Description
Empirical Responsive Images helps WordPress sites discover the image widths they
actually render on real devices. It records aggregate front-end observations, registers
matching WordPress image sizes, regenerates missing thumbnails, generates responsive
variants for local theme/plugin asset images, and can create WebP and AVIF sidecar
files when the server image editor supports those formats.
Features:
* Administrator-only front-end observer measures rendered image width, height,
viewport width, DPR, attachment ID, and local asset source URL.
* Observations are stored as aggregate size data in WordPress options.
* Observed width candidates are registered through `add_image_size()`.
* Admin batch tool regenerates image thumbnails and observed local asset variants.
* Optional WP-CLI regeneration command.
* WebP and AVIF sidecars are generated when supported by the active image editor.
* WordPress attachment images and local asset images can be wrapped in `` with AVIF/WebP sources and original fallback markup.
* Pages are kept out of page cache until a no-cache observation run confirms that
known image sizes are already represented in `srcset` output.
* No external service calls.
### Privacy
The observer runs only for logged-in users who can manage site options. Requests
require WordPress REST authentication and a valid REST nonce. It stores aggregate
rendered image data and canonical page paths only; query strings and raw IP addresses
are not persisted.
By default, settings, observations, and generated asset variants are retained when
the plugin is uninstalled. Site administrators can explicitly enable deletion under
Tools > Responsive Images before uninstalling.
### Cache compatibility
Before a page is confirmed stable, the plugin sends WordPress and HTTP cache bypass
signals:
* `DONOTCACHEPAGE`
* `Cache-Control: no-store, no-cache, must-revalidate, max-age=0`
* `CDN-Cache-Control: no-store`
* `Cloudflare-CDN-Cache-Control: no-store`
* `Surrogate-Control: no-store`
* `X-LiteSpeed-Cache-Control: no-cache`
It also disables LiteSpeed page optimization and lazy-loading constants during those
warming requests so the measured image slots match the real rendered layout.
The observer script is marked with optimizer bypass attributes including `data-cfasync
="false"`, `data-no-optimize="1"`, `data-no-defer="1"`, `data-no-minify="1"`, and`
data-pagespeed-no-defer="1"`. Its REST configuration is also duplicated into `data-
empirical-responsive-images-*` attributes so it can still run when an optimizer
delays inline scripts.
### WP-CLI
List observed sizes:
```
wp empirical-responsive-images sizes
```
Regenerate thumbnails and modern sidecars:
```
wp empirical-responsive-images regenerate --batch-size=10
```
Force rebuild:
```
wp empirical-responsive-images regenerate --force
```
## Installation
1. Upload `empirical-responsive-images` to `/wp-content/plugins/`.
2. Activate the plugin.
3. While logged in as an administrator, visit the front end on representative desktop,
tablet, and mobile widths.
4. Go to Tools > Responsive Images.
5. Review observed sizes and run thumbnail regeneration.
## FAQ
### Does this replace WordPress responsive images?
No. It adds empirical image sizes so WordPress has better candidates for its normal`
srcset` output.
### Does this use a CDN or external optimization API?
No. All work happens inside WordPress with the configured GD or Imagick image editor.
### Why are image sizes registered by width only?
Responsive `srcset` selection is width-driven. The plugin records height ranges
for visibility but registers uncropped width candidates to avoid accidental art-
direction crops.
### Does this handle theme or plugin asset images?
Yes. Manageable local `wp-content` image assets are observed, resized into `wp-content/
uploads/empirical-responsive-images/assets/`, and rewritten with empirical `srcset`
and `sizes` output.
### Does normal page rendering create image files?
No. Front-end rendering only reads variants that already exist. File generation
happens during uploads or explicit regeneration from the admin screen or WP-CLI.
### What happens to data when I uninstall the plugin?
Data is retained by default to prevent accidental loss. Enable the uninstall cleanup
setting first if you want uninstalling to remove settings, observations, and generated
local asset variants.
### Who can submit front-end observations?
Only logged-in users with the `manage_options` capability. The observer uses WordPress
cookie authentication and a REST nonce; anonymous visitors cannot submit or modify
observation data.
## Reviews
There are no reviews for this plugin.
## Contributors & Developers
“Empirical Responsive Images” is open source software. The following people have
contributed to this plugin.
Contributors
* [ Jesus Iniesta ](https://profiles.wordpress.org/jesusinica/)
[Translate “Empirical Responsive Images” into your language.](https://translate.wordpress.org/projects/wp-plugins/empirical-responsive-images)
### Interested in development?
[Browse the code](https://plugins.trac.wordpress.org/browser/empirical-responsive-images/),
check out the [SVN repository](https://plugins.svn.wordpress.org/empirical-responsive-images/),
or subscribe to the [development log](https://plugins.trac.wordpress.org/log/empirical-responsive-images/)
by [RSS](https://plugins.trac.wordpress.org/log/empirical-responsive-images/?limit=100&mode=stop_on_copy&format=rss).
## Changelog
#### 0.2.0
* Align plugin ownership metadata with WeSolvers.
* Require administrator capability and REST nonce verification for every observation
write.
* Use SiteGround Speed Optimizer’s documented public purge functions instead of
an unregistered action name.
* Use the full plugin prefix for generated image-size names and observer data attributes.
* Keep front-end rendering read-only; missing local asset variants now require
explicit regeneration.
* Prevent duplicate sidecar encoding during forced attachment regeneration.
* Serialize concurrent observation writes to prevent lost aggregate data.
* Purge a page cache when its first observation creates a blocked readiness record.
* Reject oversized or off-site observation payloads and omit query strings from
stored page keys.
* Support custom WordPress content and upload directory mappings for local assets.
* Preserve plugin data on uninstall unless an administrator explicitly opts into
deletion.
* Add PHPUnit, PHPCS, PHP compatibility, PHPStan, version-sync, CI, and package
quality gates.
#### 0.1.8
* Use WordPress’s template enhancement output buffer for full-page asset processing.
* Bound public observation rate-limit storage and retained page observations.
#### 0.1.7
* Skip alternate format sidecars for attachment sub-sizes that do not preserve
the original aspect ratio.
#### 0.1.6
* Skip alpha-flattening alternate formats for transparent source images.
#### 0.1.5
* Treat asset srcsets capped at the original source width as cache-ready.
#### 0.1.4
* Match generated asset variant URLs to the public site scheme to avoid mixed-content
requests.
#### 0.1.3
* Add static GIF asset support while skipping animated GIFs to avoid animation
loss.
#### 0.1.2
* Observe small images by default so theme asset covers, logos, and icons can be
captured.
#### 0.1.1
* Add empirical responsive variants for local theme/plugin asset images.
#### 0.1.0
* Initial release.
## Meta
* Version **0.2.0**
* Last updated **15 hours ago**
* Active installations **Fewer than 10**
* WordPress version ** 6.9 or higher **
* Tested up to **7.0.2**
* PHP version ** 7.4 or higher **
* Tags
* [AVIF](https://wordpress.org/plugins/tags/avif/)[images](https://wordpress.org/plugins/tags/images/)
[responsive images](https://wordpress.org/plugins/tags/responsive-images/)[thumbnails](https://wordpress.org/plugins/tags/thumbnails/)
[webp](https://wordpress.org/plugins/tags/webp/)
* [Advanced View](https://wordpress.org/plugins/empirical-responsive-images/advanced/)
## Ratings
No reviews have been submitted yet.
[Your review](https://wordpress.org/support/plugin/empirical-responsive-images/reviews/#new-post)
[See all reviews](https://wordpress.org/support/plugin/empirical-responsive-images/reviews/)
## Contributors
* [ Jesus Iniesta ](https://profiles.wordpress.org/jesusinica/)
## Support
Got something to say? Need help?
[View support forum](https://wordpress.org/support/plugin/empirical-responsive-images/)