Tracking region of interest

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Hey everyone,

Lets say I select a point in a live webcam and I want to track this point while the webcam is moving (eg. draw a rect around the point). The captured image should be pretty static. What approach should I follow? In the first step I want to use a webcam, later it should get replaced through a android/iOS device.

This is pretty much what solves my problem, but unfortunately it is not very stable / accurate. BTW I'm a newbie.