Demonstrates a Participants Database custom template that adds a reCAPTCHA to the Participant Login form.

pdb-login-recaptcha.php

<?php
/**
 * @version 1.0
 * 
 * the uses a recaptcha field in the login form if available
 * 
 * @global PDb_reCAPTCHA $PDb_reCAPTCHA
 */
global $PDb_reCAPTCHA;
$recaptcha_fieldname = 'captcha'; // change this to match your captcha field name
$recaptcha_field = new PDb_Field_Item( $recaptcha_fieldname );
$is_recaptcha = is_object($PDb_reCAPTCHA) && $recaptcha_field->form_element() === 'captcha' && in_array( 'recaptcha', $recaptcha_field->attributes() );
$is_invisible = $PDb_reCAPTCHA->plugin_options['size'] === 'invisible';
?>
<div id="pdbx-login" class="form-horizontal pdb-recaptcha"><?php if ( $feedback ) : ?>
  <?php echo $feedback ?>
  <?php endif ?>
  <form method="post" >
    <?php /* these hidden fields must be present */ ?>
    <input  type="hidden" name="pdbx-ser" value="<?php echo $record_page ?>" />
    <input  type="hidden" name="form" value="pdbx-login" />
    <div class="control-group">
      <label class="control-label" for="login_name" ><?php echo $this->username_field->title ?></label>
      <div class="controls">
       <input type="text" name="<?php echo $this->username_field->name ?>" value="<?php echo filter_input( INPUT_POST, $this->username_field->name, FILTER_SANITIZE_STRING )  ?>" />
      </div>
    </div>
    <?php if ( $this->showing_password_field() ) : ?>
    <?php $input_type = $this->passwords_encrypted() ? 'password' : 'text'; ?>
    <div class="control-group">
      <label class="control-label" for="login_password" ><?php echo $this->password_field->title ?></label>
      <div class="controls">
        <input type="<?php echo $input_type ?>" name="<?php echo $this->password_field->name ?>" value="" />
      </div>
    </div>
    <?php endif ?>
    <?php if ( $is_recaptcha && ! $is_invisible ) : ?>
    <div class="control-group">
      <label class="control-label" for="login_password" ><?php echo $recaptcha_field->title() ?></label>
      <div class="controls">
        <?php $recaptcha_field->print_element() ?>
      </div>
    </div>
    <?php endif ?>
    <div class="control-group">
      <div class="controls">
        <?php if ( $is_recaptcha && $is_invisible ) {
          $recaptcha_field->print_element();
        } ?>
        <input type="submit" name="submit" value="<?php echo $login_button_text ?>" /><div class="retrieve-link"><?php if ( $show_retrieve_link ) $this->print_retrieve_link() ?></div>
      </div>
    </div>
  </form>
</div>

Of course, you must be using the PDB reCAPTCHA add-on for this to work.

Make sure line 10 is correct for the name of your captcha field.

If you don't know how to use this template, read this:

Using Participants Database Custom Templates