use visual object tracking algorithm if object is not detected

[maiermic]

If object detection fails, a visual object tracking algorithm (e.g. CSRT) might be used as fallback. If object detection fails for a certain amount of consecutive frames, the object should still be considered lost.

The candidate returned from the visual object tracking algorithm might also be used/considered to re-identify the target object from the candidates of the object detection algorithm.

Useful article: https://learnopencv.com/object-tracking-using-opencv-cpp-python/
See also https://github.com/maiermic/robot-cameraman/blob/master/research.md#object-tracking-1