(Appology in advance if I am asking a too nwbie question. I am a beginner with OpenCV. I have done some tutorials yet I have not a good grasp of it\'s concepts.)
Questio
You can as well create your own cascade classifier to detect heads. The upper body is not the head at all, but just heads is not that accurate. You need to crop several number of positive samples and negative ones. Prepare list of these example in text.txt, opencv_createsamples.exe(prepare input vector for training) and use opencv_traincascade.exe command line utility to create opencv classifier for cascade detect multiscale. It is easy but the creating the dataset is time consuming. My head LBP cascade is available here for free download link to my blog for head, car and people cascade . It is compatible with detectMultiscale, but not that accurate.