import cv2

src = cv2.imread('apple.bmp', 1)
cv2.imshow('original', src)
imgray = cv2.cvtColor(src, cv2.COLOR_BGR2GRAY)
cv2.imshow('gray', imgray)

_, tresh = cv2.threshold(imgray, 127, 255, 0)
cv2.imshow('tresh', tresh)

contours, _ = cv2.findContours(tresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

cv2.drawContours(src, contours, -1, (0, 255, 0), 2)
cv2.imshow('eye', src)
cv2.waitKey(0)      
cv2.destroyAllWindows()