WordPress.org

Winsite Image Optimizer will compress your images for optimal file-size while keeping its quality (pretty much) intact, using the ImageOptim API (and other processing engines coming up soon).

You can also process all of your old images retroactively using our dedicated tool, found under the Media section.

Currently-implemented Image Processing Services:

• ImageOptim (You'll need to obtain an API key)
• Send your suggestions on our GitHub issue tracker.

Warning: This won't work on localhost in some cases, since some services work in a way that they pull images in from your site. This is why you'll need a public URL in order to make this work locally. You can use a service such as ngrok to achieve that, in conjunction with this filter:

add_filter( 'wsi_siteurl_override', function( $siteurl ) {
    return 'http://ae190611.ngrok.io/path-to-wp-installation/';
} );

We'd love to recieve contributions / suggestions from you on our GitHub project.