Object tracking after dense optical flow calculation

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Hey everyody,

I've come to the point that I've got a scene and the objects I would like to track are separated from its background and I'm calculating the optical flow of that image. Furthermore I would like to detect and track this object/blob, but I don't know what approach to choose to detect objects on top of the calculated flow.

This is a small illustration of my problem:

I'm not looking for a solution to my problem, just an approach to how I should continue. Thanks a lot for the help in advance.

Yours, Marcel