new_contents: #!/usr/bin/env python
  
  import cv
  
  class Target:
  
      def __init__(self):
          self.capture = cv.CaptureFromCAM(0)
          cv.NamedWindow("Target", 1)
  
      def run(self):
          # Capture first frame to get size
          frame = cv.QueryFrame(self.capture)
          frame_size = cv.GetSize(frame)
          color_image = cv.CreateImage(cv.GetSize(frame), 8, 3)
          grey_image = cv.CreateImage(cv.GetSize(frame), cv.IPL_DEPTH_8U, 1)
          moving_average = cv.CreateImage(cv.GetSize(frame), cv.IPL_DEPTH_32F, 3)
  
          first = True
  
          while True:
              closest_to_left = cv.GetSize(frame)[0]
              closest_to_right = cv.GetSize(frame)[1]
  
              color_image = cv.QueryFrame(self.capture)
  
              # Smooth to get rid of false positives
              cv.Smooth(color_image, color_image, cv.CV_GAUSSIAN, 3, 0)
  
              if first:
                  difference = cv.CloneImage(color_image)
                  temp = cv.CloneImage(color_image)
                  cv.ConvertScale(color_image, moving_average, 1.0, 0.0)
                  first = False
              else:
                  cv.RunningAvg(color_image, moving_average, 0.020, None)
  
              # Convert the scale of the moving average.
              cv.ConvertScale(moving_average, temp, 1.0, 0.0)
  
              # Minus the current frame from the moving average.
              cv.AbsDiff(color_image, temp, difference)
  
              # Convert the image to grayscale.
              cv.CvtColor(difference, grey_image, cv.CV_RGB2GRAY)
  
              # Convert the image to black and white.
              cv.Threshold(grey_image, grey_image, 70, 255, cv.CV_THRESH_BINARY)
  
              # Dilate and erode to get people blobs
              cv.Dilate(grey_image, grey_image, None, 18)
              cv.Erode(grey_image, grey_image, None, 10)
  
              storage = cv.CreateMemStorage(0)
              contour = cv.FindContours(grey_image, storage, cv.CV_RETR_CCOMP, cv.CV_CHAIN_APPROX_SIMPLE)
              points = []
  
              while contour:
                  bound_rect = cv.BoundingRect(list(contour))
                  contour = contour.h_next()
  
                  pt1 = (bound_rect[0], bound_rect[1])
                  pt2 = (bound_rect[0] + bound_rect[2], bound_rect[1] + bound_rect[3])
                  points.append(pt1)
                  points.append(pt2)
                  cv.Rectangle(color_image, pt1, pt2, cv.CV_RGB(255,0,0), 1)
  
              if len(points):
                  center_point = reduce(lambda a, b: ((a[0] + b[0]) / 2, (a[1] + b[1]) / 2), points)
                  cv.Circle(color_image, center_point, 40, cv.CV_RGB(255, 255, 255), 1)
                  cv.Circle(color_image, center_point, 30, cv.CV_RGB(255, 100, 0), 1)
                  cv.Circle(color_image, center_point, 20, cv.CV_RGB(255, 255, 255), 1)
                  cv.Circle(color_image, center_point, 10, cv.CV_RGB(255, 100, 0), 1)
  
              cv.ShowImage("Target", color_image)
  
              # Listen for ESC key
              c = cv.WaitKey(7) % 0x100
              if c == 27:
                  break
  
  if __name__=="__main__":
      t = Target()
      t.run()
  
subject: add track code from SO