So was <?php osc_show_recaptcha(); ?> in the file??
if not your file should look like this
<?php
/*
* Osclass – software for creating and publishing online classified
* advertising platforms
*
* Copyright (C) 2013 OSCLASS
*
* This program is free software: you can redistribute it and/or
* modify it under the terms of the GNU Affero General Public License
* as published by the Free Software Foundation, either version 3 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public
* License along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// meta tag robots
osc_add_hook('header','bender_nofollow_construct');
bender_add_boddy_class('register');
osc_enqueue_script('jquery-validate');
osc_current_web_theme_path('header.php') ;
?>
<div class="form-container form-horizontal form-container-box">
<div class="header">
<h1><?php _e('Register an account for free', 'bender'); ?></h1>
</div>
<div class="resp-wrapper">
<form name="register" action="<?php echo osc_base_url(true); ?>" method="post" >
<input type="hidden" name="page" value="register" />
<input type="hidden" name="action" value="register_post" />
<ul id="error_list"></ul>
<div class="control-group">
<label class="control-label" for="name"><?php _e('Name', 'bender'); ?></label>
<div class="controls">
<?php UserForm::name_text(); ?>
</div>
</div>
<div class="control-group">
<label class="control-label" for="email"><?php _e('E-mail', 'bender'); ?></label>
<div class="controls">
<?php UserForm::email_text(); ?>
<?php osc_show_recaptcha('register'); ?>
</div>
</div>
<div class="control-group">
<label class="control-label" for="password"><?php _e('Password', 'bender'); ?></label>
<div class="controls">
<?php UserForm::password_text(); ?>
</div>
</div>
<div class="control-group">
<label class="control-label" for="password-2"><?php _e('Repeat password', 'bender'); ?></label>
<div class="controls">
<?php UserForm::check_password_text(); ?>
<p id="password-error" style="display:none;">
<?php _e("Passwords don't match", 'bender'); ?>
</p>
</div>
</div>
<script type="text/javascript">
var RecaptchaOptions = {
theme : 'clean'
};
</script><?php osc_run_hook('user_register_form'); ?>
<?php osc_show_recaptcha(); ?>
<div class="control-group">
<div class="controls">
<button type="submit" class="ui-button ui-button-middle ui-button-main"><?php _e("Create", 'bender'); ?></button>
</div>
</div>
</form>
</div>
</div>
<?php UserForm::js_validation(); ?>
<?php osc_current_web_theme_path('footer.php') ; ?>