how to add jpg,png etc ???

{
    public function __construct()
    {
        parent::__construct( 'photoverifiUpload' );
       
        $this->setAjax( FALSE );
        $this->setAction( OW::getRouter()->urlForRoute('photoverifi.upload') );
        $this->setEnctype( Form::ENCTYPE_MULTYPART_FORMDATA );
       
        $file = new FileField( 'photo' );
        $file->setRequired();
        $file->addValidator( new JpegValidator() );
        $file->setLabel( OW::getLanguage()->text('photoverifi', 'file_label') );
        $this->addElement( $file );

        $submit = new Submit( 'send' );
        $submit->setValue( OW::getLanguage()->text('photoverifi', 'submit_btn_caption') );
        $this->addElement( $submit );
    }
   
    public function isValid( $data = NULL )
    {
        return ( !empty($_FILES['photo']) && $_FILES['photo']['error'] === 0 && $_FILES['photo']['type'] == 'image/jpeg' );
    }
}

class JpegValidator extends OW_Validator
{
    public function isValid( $value )
    {
        return preg_match( '/jpg$/', $value );
    }
   
    public function getJsValidator()
    {
        return '{
            validate : function( value )
            {
                if ( !value.match("jpg$") )
                {
                    throw OW.getLanguageText("photoverifi", "upload_type_error");
                }
            }
        }';
    }
}