how to detect moving object in live video camera using openCV

i am using openCV for my ios application to detect moving object in live video camera, but i am not familiar with use of openCV please help me. any other way to do this also welcome .

- (void)viewDidLoad {
    [super viewDidLoad];

    self.videoCamera.delegate = self;
    self.videoCamera = [[CvVideoCamera alloc] initWithParentView:self.view];

    self.videoCamera.defaultAVCaptureDevicePosition = AVCaptureDevicePositionBack;
    self.videoCamera.defaultAVCaptureSessionPreset = AVCaptureSessionPreset352x288;
    self.videoCamera.defaultAVCaptureVideoOrientation = AVCaptureVideoOrientationPortrait;
    self.videoCamera.defaultFPS = 30;
    self.videoCamera.grayscaleMode = NO;
    [self.videoCamera start];
//    cv::BackgroundSubtractorMOG2 bg;

}
- (void)processImage:(cv::Mat&)image
{
    //process here
    cv::cvtColor(image, img, cv::COLOR_BGRA2RGB);
    int fixedWidth = 270;
    cv::resize(img, img, cv::Size(fixedWidth,(int)((fixedWidth*1.0f)*   (image.rows/(image.cols*1.0f)))),cv::INTER_NEAREST);

    //update the model
   bg_model->operator()(img, fgmask, update_bg_model ? -1 : 0);


    GaussianBlur(fgmask, fgmask, cv::Size(7, 7), 2.5, 2.5);
    threshold(fgmask, fgmask, 10, 255, cv::THRESH_BINARY);

    image = cv::Scalar::all(0);
    img.copyTo(image, fgmask);
}

i am new at openCV so, i don't know what to do.

Add this code to processImage delegate :

- (void)processImage:(cv::Mat&)image
{
      //process here
      cv::cvtColor(image, img, cv::COLOR_BGRA2RGB);
      int fixedWidth = 270;
     cv::resize(img, img, cv::Size(fixedWidth,(int)((fixedWidth*1.0f)*   (image.rows/(image.cols*1.0f)))),cv::INTER_NEAREST);

    //update the model
    bg_model->apply(img, fgmask, update_bg_model ? -1 : 0);

    GaussianBlur(fgmask, fgmask, cv::Size(7, 7), 2.5, 2.5);
    threshold(fgmask, fgmask, 10, 255, cv::THRESH_BINARY);

    image = cv::Scalar::all(0);
    img.copyTo(image, fgmask);
}

You'll need to declare following as global variable

cv::Mat img, fgmask;
cv::Ptr<cv::BackgroundSubtractor> bg_model;
bool update_bg_model;
Where, img <- smaller image fgmask <- the mask denotes that where motion is happening update_bg_model <- if you want to fixed your background;

Please refer this URL for further information.