说明：  基于粒子滤波器的目标跟踪算法及C++实现，运行方式：按P停止，在前景窗口鼠标点击目标，会自动生成外接矩形，再次按P，对该选定目标进行跟踪。
(The target tracking algorithm based on particle filter and C++ implementation, operation mode: stop by P, click the target in the foreground window, automatically generate the outer rectangle, and follow P again to track the selected target.)