Python OPENCV 背景透過画像の貼り付けと場所の指定

Question

import cv2
import numpy as np

# Load two images
img1 = cv2.imread('/home/parallels/darknet/data/jimpei.jpg')
img1 = cv2.resize(img1,(1000,1000))
img2 = cv2.imread('/home/parallels/darknet/data/heart2.png')
img2 = cv2.resize(img2,(200,200))

# I want to put logo on top-left corner, So I create a ROI
rows,cols,channels = img2.shape
roi = img1[0:rows, 0:cols ]

#coordinate where to put the picture


# Now create a mask of logo and create its inverse mask also
img2gray = cv2.cvtColor(img2,cv2.COLOR_BGR2GRAY)
ret, mask = cv2.threshold(img2gray, 10, 255, cv2.THRESH_BINARY)
mask_inv = cv2.bitwise_not(mask)

# Now black-out the area of logo in ROI
img1_bg = cv2.bitwise_and(roi,roi,mask = mask_inv)

# Take only region of logo from logo image.
img2_fg = cv2.bitwise_and(img2,img2,mask = mask)

# Put logo in ROI and modify the main image
dst = cv2.add(img1_bg,img2_fg)
img1[0:rows, 0:cols ] = dst # change the coordinate #ORI 0:rows, 0:cols 
cv2.imshow('res',img1)
cv2.waitKey(0)
cv2.destroyAllWindows()

背景に背景透過した画像を重ねようと思っていて、背景透過を読み込んで貼り付けるところまでは行けました。しかし、画像を貼り付ける場所を指定する方法がわかりません。
どなたかわかるかた教えてください。