Using Captcha on testimonial submit form
To enable captcha on testimonial submit form, go to Admin->System->Configuration->Customers->Customer Configuration->CAPTCHA, select Testimonials Form in the Forms field and press Save config button.
Also you can display Captcha field by using widget. In order to show captcha in testimonial submit form , you need to include the captcha javascript to cms page. Go to Design tab of CMS page edit form. In the Layout Update XML field insert the following xml code:
<reference name="head"> <action method="addJs"><file>mage/captcha.js</file></action> </reference>
Finally press Save Page button.