jetpack_lossy_compression.php

<?php
/**
 * Plugin Name: Photon Lossy Compression
 * Plugin URI:  https://josh.blog/2015/01/lossy-compression-with-photon
 * Description: Lossy compression of images using the Jetpack Photon CDN.
 * Version:     1.0.0
 * Author:      Josh Betz
 * Author URI:  https://josh.blog
 * License:     GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */

// Photon: 80% jpeg quality
add_filter('jetpack_photon_pre_args', function( $args ) {
        $args['quality'] = 80;
        return $args;
});