image_optimizer.php

<?php
  /*
   Plugin Name: Image Optimizer
   Plugin URI:
   Description: Automatically optimizes images using jpegtran and optipng on upload
   Version: 0.1 
   Author: Scott Walkinshaw
   Author URI:
   Support URI:
   */

  class OptiImg {

    function __construct() {
      add_filter('wp_generate_attachment_metadata', array($this, 'generate_attachment_metadata'), 1);
      add_action('add_attachment', array($this, 'optimize_attachment'), 1);
    }

    /**
     * Generate attachment metadata filter
     *
     * Upload _wp_attachment_metadata
     *
     * @param array $metadata
     * @return array
     */
    public function generate_attachment_metadata($metadata) {
      $images = $this->get_metadata_files($metadata);

      foreach($images as $image) {
        $result = $this->optimize_image($image);
      }

      return $metadata;
    }

    /**
     * Returns base file path of attachment
     * @param string $attached_file
     * @return string
     */
    public function filepath($attached_file) {
      $upload_dir = wp_upload_dir();
      return $upload_dir['basedir'] . '/' . $attached_file;
    }

    /**
     * Returns array of files from sizes array
     *
     * @param string $attached_file
     * @param array $sizes
     * @return array
     */
    public function get_thumbnails($attached_file, $thumbnails) {
      $files = array();
      $base_dir = str_replace(strrchr($attached_file, '/'), '', $attached_file) . '/';
      $original_image_path = $this->filepath($attached_file);
      $files[] = $original_image_path;

      foreach ((array) $thumbnails as $thumbnail) {
        if (isset($thumbnail['file'])) {
          $files[] = $this->filepath($base_dir . $thumbnail['file']);
        }
      }

      return $files;
    }

    /**
     * Returns attachment files by metadata
     *
     * @param array $metadata
     * @return array
     */
    public function get_metadata_files($metadata) {
      $files = array();

      if (isset($metadata['file']) && isset($metadata['sizes'])) {
        $files = array_merge($files, $this->get_thumbnails($metadata['file'], $metadata['sizes']));
      }

      return $files;
    }

    /**
     * Optimize image file with jpegtran or optipng 
     *
     * @param string $image
     * @return boolean
     */
    public function optimize_image($image) {
      $type = getimagesize($image);

      if ($type !== false) {
        $type = $type['mime'];
      } else {
        return false;
      }

      switch ($type) {
        case 'image/jpeg':
        case 'image/jpg':
          exec("/usr/local/bin/jpegtran -copy none -optimize -outfile {$image} {$image}");
          break;
        case 'image/png':
        case 'image/gif':
          exec("/usr/local/bin/optipng -o7 {$image}");
          break;
        default:
          return false;
      }

      return true;
    }

    /**
     * Optimize image file by attachment id
     *
     * @param integer $attachment_id
     * @return boolean
     */
    public function optimize_attachment($attachment_id) {
      $image = get_attached_file($attachment_id);
      return $this->optimize_image($image);
    }

  }

  $opti_img = new OptiImg();

?>