Detect head using Haar Cascade, wont detect tilted head?

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Hi all,

I am very new to OpenCV and computer vision. However I have managed to make a simple android app that detects faces/eyes. I have designed a template that draws around the face, eyes, pupils and iris. The problem is, if I tilt my head slightly to one side of the other (still directly facing the camera) the detection stops. My goal of the app is to detect when the head tilts right or left to then control the scroll of a pdf file. Does anyone know why it is not detecting faces that are slightly tilted? Is there a work around or another Haar cascade I should be using? Many thanks!