General People Cascade Classifier

Hello, I'm training a Haar Cascade Classfier to identify people based on a set of samples. It works with the people from the pictures, but how can I assure that the classifier will work with different people? And what if they use different types of clothes? Is there a way to produce a general Cascade Classifier that can identify every kind of people? Here is the image I'm using:  Any tip will be very helpful, Thanks