BTImageOptimize.php

<?php
/*
Plugin Name: BT Image Optimization
Plugin URI: http://bluetent.com
Description: Provides image optimization capabilities as users upload images to the library.
Author: ethan@bluetent.com
Version: 0.1
Author URI: http://bluetent.com/
Text Domain: bt-image-optimize
License: GPLv2
*/

class BTImageOptimize {

  public function __construct() {
    add_action('add_attachment', array($this, 'attachment_optimize'));
  }

  /**
   * Performs extra processing on images.
   * @param $id int attachment_id
   */
  public function attachment_optimize($id) {
    $sizes = get_intermediate_image_sizes();
    $sizes[] = 'full';
    foreach($sizes as $size) {
      $img_src = wp_get_attachment_image_src($id, $size);
      $real_path = ABSPATH . ltrim(str_replace(get_bloginfo('url'), '', $img_src[0]), '/');
      $image_info = getimagesize($real_path);
      $p = escapeshellarg($real_path);
      $cmd = "cd " . escapeshellarg(ABSPATH) . "; ";
      switch($image_info['mime']) {
        case 'image/png':
          $cmd .= "/usr/local/bin/optipng $p";
          break;
        case 'image/jpeg':
          $cmd .= "/usr/local/bin/jpegoptim -p -m70 --strip-all $p";
          break;
      }
      if(!empty($cmd)) {
        $output = shell_exec($cmd);
      }
    }
  }
}

$BTImageOptimize = new BTImageOptimize();