Add captcha to last step of multi-step form
use this code in your template.php, you need to know what the ID of the last form is,

&lt;?php
function MYTHEME_form_alter( &amp;$form, &amp;$form_state, $form_id ){
    if ($form_id == "YOUR_FORM_ID") {
            $form['my_captcha_element'] = array(
                '#type' =&gt; 'captcha',
                '#captcha_type' =&gt; 'Math',
            );
        }
}
?&gt;


you can also replace the Math with image