title: what are values returned by findcontour function in opencv 2.4.9
body: <p>i'm using openCV 2.4.9 version and the code i was referring to had the following line:
       <code>im2,contours,hier=cv2.findContours(im_th.copy(),cv2.RETR_EXTERNAL,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)</code></p>
  
  <p>I keep getting the error : "ValuesError : need more than 2 values to unpack "
  I understand that findContour in 2.4.9 version of openCV returns only two values. But what are those values ? </p>