Fatal error: Call to undefined function exif_imagetype()

if(!function_exists('exif_imagetype')){
	function exif_imagetype($filename){
		if((list($width,$height,$type,$attr) = getimagesize($filename)) !== false ){
                    return $type;
                }
                return false;
        }
}

条件上面的代码到函数调用的地方