Title: ImReso: Unlimited Target-Size Image Compressor
Author: imageresizer
Published: August 16, 2026
Last modified: August 16, 2026
---
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# ImReso: Unlimited Target-Size Image Compressor
By [imageresizer](https://profiles.wordpress.org/imageresizer/)
[Download](https://downloads.wordpress.org/plugin/imreso-target-size-image-compressor.1.0.17.zip)
* [Details](https://wordpress.org/plugins/imreso-target-size-image-compressor/#description)
* [Reviews](https://wordpress.org/plugins/imreso-target-size-image-compressor/#reviews)
* [Installation](https://wordpress.org/plugins/imreso-target-size-image-compressor/#installation)
* [Development](https://wordpress.org/plugins/imreso-target-size-image-compressor/#developers)
[Support](https://wordpress.org/support/plugin/imreso-target-size-image-compressor/)
## Description
**ImReso is a target-size, free bulk image compressor.** It resizes and converts
your photos and images to exact pixel dimensions or a specific file size, right
in your browser — instantly. Free, unlimited and 100% privacy-first: the encoding
runs on your own device and nothing is ever uploaded. Need 50 KB or 1000px? No problem.
Most plugins in this space hand your files to a third-party server or an external
API. ImReso is different — client-side image compression, so your originals never
leave your site, with no API key, no per-file cost, no monthly cap and no bulk-job
timeout, even on the cheapest shared hosting.
Give it a size ceiling in KB and each upload is encoded to land under it automatically—
no fiddling with a quality slider. ImReso reads JPEG, PNG, WebP, AVIF, HEIC/HEIF,
TIFF and BMP, and writes WebP, AVIF or JPEG; SVG and GIF are passed through untouched
so nothing ever breaks.
It runs the same engine as **[ImageResizer.cc](https://imageresizer.cc/)**, the
free online tool by the same team. Need to handle a one-off file without opening
WordPress? Use the web app at **[imageresizer.cc/app](https://imageresizer.cc/app)**—
same engine, any browser, nothing uploaded.
#### What makes it different
* **Zero server load** — all the work runs in the browser via WebAssembly, so nothing
times out and your host isn’t taxed, even on cheap shared hosting.
* **Nothing is uploaded** — your originals never leave the site; the browser does
all the work.
* **No API key, no signup, no limits** — no credits to buy, no monthly quota, no
account. Free, unlimited image compression, always.
* **Target file size** — hit an exact size (100, 300, 500 KB…), not just a guessed
quality value.
* **Max width** — scale huge photos down to a longest-edge cap before they are
stored.
* **HEIC to WebP or AVIF** — turn iPhone photos and other heavy formats into modern,
lighter ones on upload.
* **Leaner thumbnails** — the sub-sizes WordPress builds on the server use your
chosen quality too.
* **Works everywhere** — Safari, iOS and every modern browser; fully translatable,
with language packs delivered by WordPress.
#### How you use it
You don’t. Upload the way you already do — the plugin works on the upload itself,
so there is no button to press, no queue to start and no bulk job to babysit.
Drop files into the Media Library as usual and each one is compressed in your browser
before WordPress stores it. Writing a post is the same: add an Image block, upload,
and the file that lands on your site is already the smaller one — the original never
leaves your computer.
Set the target size and format once in the ImReso menu and you can forget about
it. The screenshots below show both, alongside the dashboard that adds up what you
saved.
#### Supported formats
* **Read / resize / compress:** JPEG, PNG, WebP, AVIF, BMP, TIFF.
* **Read & convert to a web format:** HEIC / HEIF (iPhone), plus TIFF and BMP.
* **Output:** WebP, AVIF or JPEG (chosen automatically or fixed in settings).
* **Left untouched (uploaded as-is):** GIF, whether animated or not (re-encoding
would drop frames), SVG (vector), ICO and JPEG 2000. These are uploaded unchanged
so nothing is ever broken.
* **Already small:** a JPEG, PNG, WebP or AVIF under 10 KB is left alone — re-encoding
one rarely saves anything and can cost you quality. HEIC, TIFF and BMP are always
converted, whatever their size, because the point there is a web-friendly format
rather than a smaller file. So a tiny test image is _expected_ to come through
untouched.
#### What gets optimized
Uploads on the media and editor screens: the **classic Media Library** (`upload.
php`), the **Add New Media** screen, the **“Add Media” dialog and Media Library
popup**, and **inline uploads in the block (post/page) editor** — drag-and-drop,
paste, and the block “Upload” button.
Everywhere the block editor runs is covered, so that also includes the **Site Editor**
on a block theme and the block **widgets** screen on a classic one.
Programmatic / REST / WP-CLI / FTP uploads cannot be processed by any client-side
tool, including this one.
#### About ImageResizer.cc
This plugin is made by the team behind **[ImageResizer.cc](https://imageresizer.cc/)**—
a free, privacy-first online tool to resize, compress and convert images entirely
in the browser. The plugin brings that same engine straight into your WordPress
upload flow.
Working outside WordPress? The web app handles the same jobs with no install: [compress an image to a target size](https://imageresizer.cc/app),
convert HEIC to JPG, or convert PNG to WebP — all client-side, nothing uploaded,
no account.
#### Source code
Nothing in this plugin is obfuscated. The files under `build/` are minified for
delivery only. The complete, un-minified sources that produce them ship inside the
plugin, and the same tree is public at
https://github.com/AlexStack/imreso-target-size-image-compressor
What ships:
* `src-js/` — every TypeScript/JavaScript source file (worker engine, main-thread
client, uploader interceptors, format sniffer). `build/ir-worker.js`, `build/
worker-client.js`, `build/classic-uploader.js` and `build/block-uploader.js`
are built from these.
* `build.mjs` — the esbuild configuration that bundles `src-js/` into `build/`.
* `package.json` — declares the third-party packages listed below. The versions
the shipped `build/` was produced from are recorded in `licenses/README.txt`.
* build/chunks/ holds the lazily loaded pieces esbuild split out. They are minified
derivatives, not verbatim copies, and they come from three places:
* **Third-party** — `encode-*.js`, `avif_enc-*.js`, `webp_enc-*.js` and `webp_enc_simd-*.
js` are the @jsquash codecs; `UTIF-*.js` is utif2 (which bundles pako); `heic-
to-*.js` is heic-to, and at ~3 MB it is the largest file in the plugin — it is
libheif compiled to plain JavaScript, so HEIC decoding needs no extra binary.
The readable originals are the npm packages listed under “Third-party libraries”
below, reproduced verbatim by `npm install`; their full licence texts ship in`
licenses/`.
* **Ours** — one `chunk-*.js` is built from `src-js/wfd-shim.js`.
* **Generated by the build** — another `chunk-*.js` carrying esbuild’s own CommonJS
interop runtime, and `avif_enc_mt-*.js`, a one-line stub `build.mjs` substitutes
for the multi-threaded AVIF codec so it is never bundled.
The eight-character hash in each chunk filename is content-derived, so these exact
names change whenever a dependency does.
To regenerate everything in `build/` from those sources, run this from the plugin
folder:
```
npm install && npm run build
```
The rebuilt `build/` is functionally identical. The four `.wasm` codecs and the
four top-level bundles come out byte-for-byte the same. The lazily loaded files
under `build/chunks/` carry an esbuild content hash in their filename (`heic-to-
.js`); that hash is derived from the chunk’s contents, so it moves whenever
a dependency version does, and the import statements in `ir-worker.js` move with
it. The chunk contents are unchanged and each `build/` is internally consistent.
The hash is what stops browsers serving a stale chunk after a plugin update.
#### The .wasm files
```
build/ contains four WebAssembly binaries. They are the image encoders themselves — the plugin exists to compress images on the user's own device instead of on a server or an external API, and these are what performs that encoding. Without them the plugin has no function at all.
```
They are the stock, unmodified binaries published by the `@jsquash` packages: `npm
install` fetches byte-identical files and `build.mjs` copies them next to the bundle.
Nothing is fetched at runtime — they are loaded from the plugin folder, which is
what keeps every image on the user’s own device.
Each is compiled from a public, GPL-compatible upstream C/C++ project:
* `webp_enc.wasm`, `webp_enc_simd.wasm` — libwebp (BSD-3-Clause) — https://chromium.
googlesource.com/webm/libwebp
* `mozjpeg_enc.wasm` — mozjpeg (BSD-3-Clause / IJG) — https://github.com/mozilla/
mozjpeg
* `avif_enc.wasm` — libavif (BSD-2-Clause) — https://github.com/AOMediaCodec/libavif—
with libaom — https://aomedia.googlesource.com/aom
The build scripts that produce these binaries from those sources are published by
jSquash:
https://github.com/jamsinclair/jSquash
#### Third-party libraries
This plugin bundles the following GPL-compatible open-source libraries. The full
text of each licence ships in the plugin’s `licenses/` directory, with the exact
bundled versions; upstream sources are linked below.
* **@jsquash/avif**, **@jsquash/webp**, **@jsquash/jpeg** — Apache-2.0 — WebAssembly
image codecs — https://github.com/jamsinclair/jSquash
* **heic-to** — LGPL-3.0 — HEIC/HEIF decoding (wraps libheif) — https://github.
com/hoppergee/heic-to
* **utif2** — MIT — TIFF decoding — https://github.com/photopea/UTIF.js
* **pako** — MIT AND Zlib — zlib inflate, bundled inside utif2 — https://github.
com/nodeca/pako
The codec binaries these packages ship are compiled from **libwebp** (BSD-3-Clause),**
mozjpeg** (BSD-3-Clause / IJG), **libavif** + **libaom** (BSD-2-Clause with the
Alliance for Open Media patent grant) and **libheif** (LGPL-3.0).
Because libheif and heic-to are LGPL-3.0, the combined work is distributed under**
GPLv3** as permitted by this plugin’s “GPLv2 or later” licence.
## Screenshots
[⌊Set it once — an output format, a size ceiling in KB, a maximum dimension and
a quality — then forget about it. Every upload is encoded to land under that ceiling
on its own, with no quality slider to guess at.⌉⌊Set it once — an output format,
a size ceiling in KB, a maximum dimension and a quality — then forget about it.
Every upload is encoded to land under that ceiling on its own, with no quality slider
to guess at.⌉[
Set it once — an output format, a size ceiling in KB, a maximum dimension and a
quality — then forget about it. Every upload is encoded to land under that ceiling
on its own, with no quality slider to guess at.
[⌊What it saved you, image by image: what the file was, what it became, and the
percentage off. The running total sits at the top of the same screen.⌉⌊What it saved
you, image by image: what the file was, what it became, and the percentage off.
The running total sits at the top of the same screen.⌉[
What it saved you, image by image: what the file was, what it became, and the percentage
off. The running total sits at the top of the same screen.
[⌊Writing a post is unchanged. Add an Image block and upload — the file that reaches
your site is already the smaller one, because the encoding happened on your own
machine first.⌉⌊Writing a post is unchanged. Add an Image block and upload — the
file that reaches your site is already the smaller one, because the encoding happened
on your own machine first.⌉[
Writing a post is unchanged. Add an Image block and upload — the file that reaches
your site is already the smaller one, because the encoding happened on your own
machine first.
[⌊The Media Library works the same way, a whole batch at a time. Nothing queues
on your server, so nothing times out however many files you drop in.⌉⌊The Media
Library works the same way, a whole batch at a time. Nothing queues on your server,
so nothing times out however many files you drop in.⌉[
The Media Library works the same way, a whole batch at a time. Nothing queues on
your server, so nothing times out however many files you drop in.
## Installation
1. Upload the `imreso-target-size-image-compressor` folder to `/wp-content/plugins/`,
or install the .zip via Plugins Add New Upload Plugin.
2. Activate the plugin.
3. Go to **the ImReso menu** and adjust the **ImReso** options (format, quality, max
dimension) if you like — sensible defaults are set automatically.
4. Upload images through the Media Library — they are resized and compressed in your
browser before they are stored.
## FAQ
### Can I bulk compress and resize images?
Yes. Select as many images as you like in the Media Library or “Add Media” dialog
and each one is resized and compressed in your browser before upload. There is no
per-image limit and nothing is queued on a server.
### Can I compress to a specific file size?
Yes. Set the “Max compress size” in the ImReso menu (default 500 KB) and the plugin
searches the encoder quality so each image lands at about that size. Set it to 0
to use a fixed Quality value instead.
### Can I compress images without a server or external API?
Yes — that is the whole point. All processing happens in your browser, so the free
plugin makes **zero external network requests**. Your images are never sent to our
servers or anyone else’s.
### Is there a limit on how many images I can optimize?
No. It is genuinely unlimited — there is nothing to meter because the work runs
on your own device.
### Which image formats are supported?
It reads JPEG, PNG, WebP, AVIF, BMP, TIFF and HEIC/HEIF, and outputs WebP, AVIF
or JPEG. GIF (animated or not), SVG, ICO and JPEG 2000 are left untouched and uploaded
as-is.
### Can it handle iPhone HEIC photos?
Yes. HEIC/HEIF images are decoded and converted to WebP, AVIF or JPEG entirely in
your browser, so they’re viewable everywhere, and it is the converted file that
gets stored — WordPress never sees the HEIC.
The conversion needs JavaScript. If it cannot run, the plugin steps aside and the
browser posts the original file; the plugin allows `.heic`/`.heif` through the upload
filter so that attempt is not blocked, but whether a raw HEIC is accepted and thumbnailed
after that is up to your server’s image library, and many do not support it.
### Does it optimize images already in my Media Library?
Not yet. This release resizes and compresses **new uploads**. Bulk optimization
of the existing library is planned for a later release.
### AVIF seems slow on my phone.
AVIF encoding is CPU-heavy. On mobile devices the plugin automatically prefers WebP
for reliability. You can also fix the format to WebP in the ImReso menu.
### My browser console says “wasm streaming compile failed”. Is something broken?
No — images still compress, and you can confirm it from the savings figures. Some
hosts (a few nginx setups in particular) do not yet map the `.wasm` extension to
the `application/wasm` content type. When that happens the browser refuses to compile
the codec while it downloads and falls back to loading it into memory first, which
is a little slower on the very first image of a page and logs that message. The
codecs are read from this plugin’s own folder either way; nothing is fetched from
anywhere else. Adding `application/wasm wasm;` to your server’s mime types removes
the message.
### What happens if compression fails or doesn’t help?
The original file is uploaded unchanged. Compression never blocks or breaks an upload.
### Does the plugin update automatically?
Yes. Updates are delivered by WordPress.org like any other plugin from the directory—
you will see them on the Plugins screen, and you can switch on “Enable auto-updates”
there to have them installed for you. The plugin ships no updater of its own and
contacts no server to check for updates.
### What languages is the plugin available in?
Every string in the interface is translatable, and translations are delivered by
WordPress itself: once your site’s locale has been translated on translate.wordpress.
org, WordPress installs and updates the language pack for you, with no action needed
here. Contributions for any locale are welcome there — the project page is linked
from this plugin’s page in the plugin directory.
## Reviews
There are no reviews for this plugin.
## Contributors & Developers
“ImReso: Unlimited Target-Size Image Compressor” is open source software. The following
people have contributed to this plugin.
Contributors
* [ imageresizer ](https://profiles.wordpress.org/imageresizer/)
[Translate “ImReso: Unlimited Target-Size Image Compressor” into your language.](https://translate.wordpress.org/projects/wp-plugins/imreso-target-size-image-compressor)
### Interested in development?
[Browse the code](https://plugins.trac.wordpress.org/browser/imreso-target-size-image-compressor/),
check out the [SVN repository](https://plugins.svn.wordpress.org/imreso-target-size-image-compressor/),
or subscribe to the [development log](https://plugins.trac.wordpress.org/log/imreso-target-size-image-compressor/)
by [RSS](https://plugins.trac.wordpress.org/log/imreso-target-size-image-compressor/?limit=100&mode=stop_on_copy&format=rss).
## Changelog
#### 1.0.17
* The plugin directory strips images out of a description, so the ones added in
1.0.16 rendered as nothing and took their captions with them, leaving gaps in
the text. Removed them and wrote the copy where the directory does show a picture:
the screenshot captions.
#### 1.0.16
* Listing page: the settings and savings screens now appear at the top of the description,
and a “How you use it” section shows what uploading looks like in the Media Library
and the post editor.
* Cropped the two upload screenshots to their content — two thirds of one of them
was empty margin, which made the annotations hard to read at the width the directory
renders them.
#### 1.0.15
* Fixed the repository link in this readme. It was wrapped in bold markers, and
link checkers were reading those as part of the address, so the link resolved
to a 404 even though the repository is public.
* Added `build/README.txt`: a plain-text manifest naming the source of every generated
file, so the origin of anything under `build/` can be read without leaving that
directory.
#### 1.0.14
* Uploads in the **Site Editor** and on the block **widgets** screen are now compressed
too. On a block theme those are the main places images get added, and they were
the last admin screens left uncovered.
* Documented that files under 10 KB are left alone, so a small test image coming
through untouched is expected rather than a fault.
* Clarified what happens to an iPhone HEIC when JavaScript cannot run.
#### 1.0.13
* Fixed: images uploaded on the “Add New Media” screen were compressed correctly
but their savings never reached the dashboard or the Media Library’s “Optimized”
column. That screen returns the new attachment’s id in a different shape from
the Media Library grid, and only the grid’s shape was being read.
#### 1.0.12
* First public release.
* Compresses and resizes images entirely in the browser as you upload them, to
a target file size or a maximum dimension, with no server work and no external
requests.
* Reads JPEG, PNG, WebP, AVIF, HEIC/HEIF, TIFF and BMP; writes WebP, AVIF or JPEG.
GIF, SVG, ICO and JPEG 2000 are passed through untouched.
* Server-generated thumbnail sizes reuse your chosen quality.
* Savings dashboard with per-image before/after figures, and an “Optimized” column
in the Media Library.
* Translations are delivered by WordPress from translate.wordpress.org; contributions
for any locale are welcome there.
Versions 1.0.0 to 1.0.11 were pre-release builds that were never published to the
WordPress.org directory. Their history is in the public repository.
## Meta
* Version **1.0.17**
* Last updated **18 hours ago**
* Active installations **Fewer than 10**
* WordPress version ** 6.5 or higher **
* Tested up to **7.0.4**
* PHP version ** 7.4 or higher **
* Tags
* [compress images](https://wordpress.org/plugins/tags/compress-images/)[heic](https://wordpress.org/plugins/tags/heic/)
[image compressor](https://wordpress.org/plugins/tags/image-compressor/)[Photo Compressor](https://wordpress.org/plugins/tags/photo-compressor/)
* [Advanced View](https://wordpress.org/plugins/imreso-target-size-image-compressor/advanced/)
## Ratings
No reviews have been submitted yet.
[Your review](https://wordpress.org/support/plugin/imreso-target-size-image-compressor/reviews/#new-post)
[See all reviews](https://wordpress.org/support/plugin/imreso-target-size-image-compressor/reviews/)
## Contributors
* [ imageresizer ](https://profiles.wordpress.org/imageresizer/)
## Support
Got something to say? Need help?
[View support forum](https://wordpress.org/support/plugin/imreso-target-size-image-compressor/)