    public function update() {

        //populate the alt tag field if the user didn't
        if (empty($this->params['alt'])) $this->params['alt'] = $this->params['title'];

        // call expController update to save the image
        parent::update();
    }
The software constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.