使用OpenCV检测的最佳标记类型是什么？如何在iPhone上实时找到2D位置？

I am writing an iPhone app to use OpenCV to detect the 2D location in the iPhone camera of some sort of predefined marker (only one). What is the best type of marker? Circle? Square? Color? What is the fastest way to detect that marker? In addition, the detection algorithm needs to run near real-time.I am writing an iPhone app to use OpenCV to det