OpenCV imshow in Boost Threads

Question

Below is the code for a tracking module. A detector is launched and when it detects the object of interest, it creates a tracker object to track the object using camshift on a number of frames until the detector finds another object. The code seems to work fine when I comment out imshow and waitkey in the tracker. But when I call those functions, I get the following error when a new tracker (apart from the first one) is created:

QMetaMethod::invoke: Unable to invoke methods with return values in queued connections
QObject::startTimer: QTimer can only be used with threads started with QThread

I don't know if this is something happening within boost or opencv. Any ideas how I can fix this problem? Is there a better way to go about showing the user the position of the object of interest? Thanks a lot!

main:

#define FACE_DETECT_RATE 10
Tracker *currentTracker;

boost::mutex displayedImageMutex;
Mat imageToShow;     // image displayed by the main thread

void updateDisplayedImage(Mat image){
    if (displayedImageMutex.try_lock()){
       image.copyTo(imageToShow);
       displayedImageMutex.unlock()
    }
}

Rect detectorCallback(Rect faceRect){
    // the detector object returns the face it found here
    //  a tracker is supposed to track the face in the next set of frames
    Tracker tracker(faceRect);
    tracker.start(&updateDisplayedImage);
    currentTracker = &tracker;
    currentTracker->join();
}

int main(int argc, char **argv){
    VideoCapture capture(0);
    currentTracker = NULL;

    int frameCount = 0;

    while (true){
        Mat frame;
        capture >> frame;

        if (frameCount % FACE_DETECT_RATE == 0){
            Detector detector;
            detector.start(frame, &detectorCallback);
        }

        if (displayedImageMutex.try_lock()){
            if (imageToShow.data){
                imshow("Results", imageToShow);
                waitKey(1);
            }
            displayedImageMutex.unlock();
        }
    }
}

Tracker:

class Tracker{
private:
    boost::thread *trackerThread;

    void run(void (*imageUpdateFunc)(Mat)){
        while (true){
            try{
                ...
                //do camshift and stuff

                //show results
                //imshow("Stream", imageWithFace);
                //waitKey(10);
                imageUpdateFunc(imageWithFace);
                ...
                boost::this_thread::interruption_point();

            } catch (const boost::thread::interrupted&){
                break;
            }
        }
    }


public:
    Tracker(Rect faceRect){
        ...
    }   

    void start(void (*imageUpdateFunc)(Mat)){
        trackerThread = new boost::thread(&Tracker::run, this, imageUpdateFunc);
    }

    void stop(){
        trackerThread->interrupt();
    }

    void join(){
        trackerThread->join();
    }
};