Как увеличить найденный объект и обрезать фотографию?

Программа находит объект и выделяет его, но не получается обрезать фотографию по контуру.

import numpy as np
import cv2
from matplotlib import pyplot as plt
MIN_MATCH_COUNT = 10
img1 = cv2.imread('123.jpg',0)          # queryImage
img2 = cv2.imread('345.jpg',0) # trainImage
sift = cv2.xfeatures2d.SIFT_create()
kp1, des1 = sift.detectAndCompute(img1,None)
kp2, des2 = sift.detectAndCompute(img2,None)
FLANN_INDEX_KDTREE = 1
index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5)
search_params = dict(checks = 50)
flann = cv2.FlannBasedMatcher(index_params, search_params)
matches = flann.knnMatch(des1,des2,k=2)
good = []
for m, n in matches:
     if m.distance < 0.7*n.distance:
        good.append(m)

if len(good)>MIN_MATCH_COUNT:
     src_pts = np.float32([ kp1[m.queryIdx].pt for m in good 
]).reshape(-1,1,2)
     dst_pts = np.float32([ kp2[m.trainIdx].pt for m in good  
]).reshape(-1,1,2)
    M, mask = cv2.findHomography(src_pts, dst_pts, cv2.RANSAC,5.0)
    matchesMask = mask.ravel().tolist()
    h, w = img1.shape
    pts = np.float32([ [0,0],[0,h-1],[w-1,h-1],[w-1,0] 
]).reshape(-1,1,2)
    dst = cv2.perspectiveTransform(pts,M)
    img2 = cv2.polylines(img2,[np.int32(dst)],True,255,3, 
cv2.LINE_AA)
else:
    print( "Not enough matches are found - {}/{}".format(len(good), 
MIN_MATCH_COUNT) )
    matchesMask = None

draw_params = dict(matchColor = (0,255,0),
               singlePointColor = None,
               matchesMask = matchesMask, 
               flags = 2)
img3 = cv2.drawMatches(img1,kp1,img2,kp2,good,None,**draw_params)
plt.imshow(img3, 'gray'),plt.show()
cv2.imwrite('Image.jpg', img2)