Watermarking uploads in WordPress with Imagemagick

class-watermark-image.php

function register_watermarked_size() {
  add_image_size( 'watermarked', 550, 550, true ); // This is what should be uploaded
}
add_action( 'init', 'register_watermarked_size' );

class Watermark_Image {

  // The attachment meta array
  public $meta = array();

  // The upload dir (including year and month)
  private $upload_dir = '';

  // The path to the uploaded and unprocessed file
  private $uploaded_file_path = '';

  public function __construct($meta) {

    $this->meta = $meta;

    $this->generate();

  }

  public function get_meta() {
    return $this->meta;
  }

  public function generate() {

    $time = substr( $this->meta['file'], 0, 7 );
    $this->upload_dir = wp_upload_dir( $time );

    $filename = $this->meta['sizes']['watermarked']['file'];

    $this->uploaded_file_path = trailingslashit( $this->upload_dir['path'] ) . $filename;

    $this->watermark_image();

  }

  private function watermark_image() {

    $image_resource = new Imagick( $this->uploaded_file_path );
    $image_resource->blurImage( 20, 10 );

    $watermark_resource = new Imagick( get_stylesheet_directory() . '/images/codeable-logo.png' );
    $image_resource->compositeImage( $watermark_resource, Imagick::COMPOSITE_DEFAULT, 100, 250 );

    $this->save_image( $image_resource );

  }

  private function save_image( $image_resource ) {

    $image_data = pathinfo( $this->uploaded_file_path );

    $watermarked_filename = $image_data['filename'] . '-watermarked.' . $image_data['extension'];

    $watermarked_file_path = str_replace( $image_data['basename'], $watermarked_filename, $this->uploaded_file_path );

    if ( ! $image_resource->writeImage( $watermarked_file_path ) )
      return $image_data['basename'];

    unlink( $this->uploaded_file_path ); // Because that file isn't referred to anymore

    $this->meta['sizes']['watermarked']['file'] = $watermarked_filename;

  }

}

function generate_watermarked_image( $meta ) {

  $watermark_image = new Watermark_Image( $meta );
  $meta = $watermark_image->get_meta();

  return $meta;

}
add_filter( 'wp_generate_attachment_metadata', 'generate_watermarked_image' );

watermark-image.php

function register_watermarked_size() {
  add_image_size( 'watermarked', 550, 550, true ); // This is what should be uploaded
}

add_action( 'init', 'register_watermarked_size' );

function generate_watermarked_image( $meta ) {

  $time = substr( $meta['file'], 0, 7); // Extract the date in form "2015/04"
  $upload_dir = wp_upload_dir( $time ); // Get the "proper" upload dir

  $filename = $meta['sizes']['watermarked']['file'];
  $meta['sizes']['watermarked']['file'] = watermark_image( $filename, $upload_dir );

  return $meta;

}

add_filter( 'wp_generate_attachment_metadata', 'generate_watermarked_image' );

function watermark_image( $filename, $upload_dir ) {

  $original_image_path = trailingslashit( $upload_dir['path'] ) . $filename;

  $image_resource = new Imagick( $original_image_path );
  $image_resource->blurImage( 20, 10 );

  $watermark_resource = new Imagick( get_stylesheet_directory() . '/images/codeable-logo.png' );
  $image_resource->compositeImage( $watermark_resource, Imagick::COMPOSITE_DEFAULT, 100, 250 );

  return save_watermarked_image( $image_resource, $original_image_path );

}

function save_watermarked_image( $image_resource, $original_image_path ) {

  $image_data = pathinfo( $original_image_path );

  $new_filename = $image_data['filename'] . '-watermarked.' . $image_data['extension'];

  $watermarked_image_path = str_replace($image_data['basename'], $new_filename, $original_image_path);

  if ( ! $image_resource->writeImage( $watermarked_image_path ) )
    return $image_data['basename'];

  unlink( $original_image_path ); // Because that file isn't referred to anymore

  return $new_filename;

}

I have a StackOverflow question about how to improve this here: http://stackoverflow.com/questions/34377231/wordpress-blur-image-on-upload