public function init()
 {
     parent::init();
     $element = new Zend_Form_Element_Checkbox('useExisting');
     $element->setRequired(true);
     $element->setValue(1);
     $element->setLabel('Use existing image:');
     $this->useExisting = $element;
     $this->addElement('hidden', 'existingFilename', array('required' => true, 'ignore' => false, 'decorators' => array('ViewHelper')));
 }