image: Matrix of the type CV_8U containing an image where objects are detected.
objects: Vector of rectangles where each rectangle contains the detected object, the rectangles may be partially outside the original image.
numDetections: Vector of detection numbers for the corresponding objects. An object's number of detections is the number of neighboring positively classified rectangles that were joined together to form the object.
对于这个rejectleves、levelweights 文档给出的解释是：
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. if outputRejectLevels is true returns rejectLevels and levelWeights
