captcha for event submission form

<?php
/*
This snippet will allow Really Simple Captcha to work with the Events Manager event submission formss

Instructions:
1. Download and Install -> http://wordpress.org/extend/plugins/really-simple-captcha/
2. Add this code to your site, such as pasting the contents of this into a new php file and place it in the wp-content/mu-plugins folder. See here for instructions - http://wp-events-plugin.com/tutorials/how-to-safely-add-php-code-to-wordpress/
*/

function em_validate_event_form($result){
  global $EM_Event,$EM_Notices;
  $captcha_instance = new ReallySimpleCaptcha();
  $captcha_instance_correct = false;
  $captcha_instance_prefix = $_REQUEST['captcha_instance_prefix'];
  $captcha_instance_code = $_REQUEST['captcha_instance_code'];
  $captcha_instance_check = $captcha_instance->check( $captcha_instance_prefix, $captcha_instance_code );
  $captcha_instance_correct = $captcha_instance_check;
  if ( !$captcha_instance_correct && !is_user_logged_in() ){
    $EM_Notices->add_error('Invalid security code');
    return false;
  }
  return $result;
}
add_filter('em_event_validate','em_validate_event_form');

function my_em_event_form_captcha(){
  if ( !is_user_logged_in() ){
    $captcha_instance = new ReallySimpleCaptcha();
    $captcha_instance->chars = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789';
    $captcha_instance->char_length = '4';
    // Width/Height dimensions of CAPTCHA image.
    $captcha_instance->img_size = array( '72', '24' );
    // Font color of CAPTCHA characters, in RGB (0 - 255).
    $captcha_instance->fg = array( '0', '0', '0' );
    // Background color of CAPTCHA image, in RGB (0 - 255).
    $captcha_instance->bg = array( '255', '255', '255' );
    // Font Size of CAPTCHA characters.
    $captcha_instance->font_size = '16';
    // Width between CAPTCHA characters.
    $captcha_instance->font_char_width = '15';
    // CAPTCHA image type. Can be 'png', 'jpeg', or 'gif'
    $captcha_instance->img_type = 'png';
    $captcha_instance_word = $captcha_instance->generate_random_word();
    $captcha_instance_prefix = mt_rand();
    $captcha_instance_image_name = $captcha_instance->generate_image($captcha_instance_prefix, $captcha_instance_word);
    $captcha_instance_image_url =  get_bloginfo('wpurl') . '/wp-content/plugins/really-simple-captcha/tmp/';
    $captcha_instance_image_src = $captcha_instance_image_url.$captcha_instance_image_name;
    $captcha_instance_image_width = $captcha_instance->img_size[0];
    $captcha_instance_image_height = $captcha_instance->img_size[1];
    $captcha_instance_field_size = $captcha_instance->char_length;
    $captcha_instance_form_label = 'Anti-Spam:';
    ?>
    <p class="comment-form-captcha">
      <img src="<?php echo $captcha_instance_image_src; ?>" alt="captcha" width="<?php echo $captcha_instance_image_width; ?>" height="<?php echo $captcha_instance_image_height; ?>" />
      <label for="captcha_code"><?php echo $captcha_instance_form_label; ?></label>
      <input id="captcha_instance_code" name="captcha_instance_code" size="<?php echo $captcha_instance_field_size; ?>" type="text" />
      <input id="captcha_instance_prefix" name="captcha_instance_prefix" type="hidden" value="<?php echo $captcha_instance_prefix; ?>" />
    </p>
    <?php
  }
}
add_action('em_front_event_form_footer','my_em_event_form_captcha');