Objects Detection in python opencv

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I am trying to detect the objects in an image and then making a rectangle around it. I followed the opencv docs and didn't got the desire output.

My code is :

import numpy as nm 
import cv2

im=cv2.imread('4.jpg')

imgray=cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)

ret,thresh = cv2.threshold(imgray,127,255,0)

contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

cnt=contours[0]

cv2.drawContours(thresh,contours,-1,(0,255,0),10)

x,y,w,h=cv2.boundingRect(cnt)

cv2.rectangle(imgray,(x,y),(x+w,y+h),(0,255,0),10)

print x,y,w,h

cv2.imshow('image',imgray)

cv2.waitKey(0)

cv2.destroyAllWindows()

Input :

Output: