Marko Heijnen

CodeKitchen

DH-Shredder

In WordPress 3.5 all of the GD functionality has been abstracted out and with that power Imagick has been including to WordPress 3.5 too. Gmagick needs to wait a little bit more but with this plugin you can already use it.
If you want to know a little bit more about the changes you can look at: 
* https://make.wordpress.org/core/2012/12/06/wp_image_editor-is-incoming/ 
* http://markoheijnen.com/wordpress-new-image-manipulation/ 
* http://www.slideshare.net/markoheijnen/image-manipulation-in-wordpress-35

Gmagick

ShortPixel

reSmush.it

The reSmush.it Image Optimizer is a free WordPress image compressor and optimizer plugin which allows you to smush your website’s images so that they load faster. 
The plugin is super easy to use (just 2 clicks!), supports JPG, PNG and GIF image formats and can be used to bulk optimize current (past) images and automatically optimize all new images. 
You can also adjust the optimization levels and exclude certain images. 
Since its launch more than 9 years ago, <a href="https://resmush.it" rel="nofollow ugc">reSmush.it</a> has become the preferred choice for WordPress image optimization as it allows you to smush the images for free. 
reSmush.it image optimization service works on <a href="https://resmush.it/tools/" rel="nofollow ugc">various CMS platforms</a> (WordPress, Drupal, Joomla, Magento, Prestashop, etc.) and is used by more than 400,000 websites worldwide. 
reSmush.it has earned the reputation of being the best free, fast and easy image optimization plugin out there 🙂
Features: 
– Free bulk image compressor 
– Automatic image optimization on upload 
– Keep or remove EXIF data 
– Image quality selector 
– Exclude images from optimization 
– Powerful and free image optimizer API 
– Customizable settings for image quality 
– Automatic image optimization with CRON 
– Backup and restore original images 
– Image statistics 
– File logging for developers
Other plugins by <a href="https://shortpixel.com" rel="nofollow ugc">ShortPixel</a>:
<ul>
<li><a href="https://wordpress.org/plugins/fastpixel-website-accelerator/" rel="ugc">FastPixel Caching</a> – WP Optimization made easy</li>
<li><a href="https://wordpress.org/plugins/shortpixel-image-optimiser/" rel="ugc">ShortPixel Image Optimizer</a> – Image optimization & compression for all the images on your website, including WebP & AVIF delivery</li>
<li><a href="https://wordpress.org/plugins/shortpixel-adaptive-images/" rel="ugc">ShortPixel Adaptive Images</a> – On-the-fly image optimization & CDN delivery</li>
<li><a href="https://wordpress.org/plugins/enable-media-replace/" rel="ugc">Enable Media Replace</a> – Easily replace images or files in Media Library</li>
<li><a href="https://wordpress.org/plugins/regenerate-thumbnails-advanced/" rel="ugc">reGenerate Thumbnails Advanced</a> – Easily regenerate thumbnails</li>
<li><a href="https://wordpress.org/plugins/resize-image-after-upload/" rel="ugc">Resize Image After Upload</a> – Automatically resize each uploaded image</li>
<li><a href="https://wordpress.org/plugins/wp-svg-images/" rel="ugc">WP SVG Images</a> – Secure upload of SVG files to Media Library</li>
</ul>

reSmush.it : The original free image compressor and optimizer plugin

the plugin is great, but the service itself is remote so you depend on the network, this causes many stability issues and in the past weeks ițs been horrible.

many stability

Unfortunately I had a lot of problems with resmush.it. Even running it on a fairly new and clean website with few other plugins. 

1. Resmush.it constantly had problems connecting to a server.

2. When I tried uploading an image I sometimes had to wait for minutes before smushed it. I don't know whether it had anything to do with the server connection issue.

3. When I tried to recreate all images it broke the site after which I had to install the site from a backup. The fact that there is an admin notice saying to backup the whole site before doing that only means that this is a common issue.

All in all I had very bad experience with the plugin and I don't recommend it to anyone.

Only problems

reSmush.it is the FREE image compressor and optimizer plugin - use it to optimize your images and improve the SEO and performance of your website.

Gmagick vs reSmush.it : The original free image compressor and optimizer plugin