How to subtract two images using python opencv2 to get the foreground object

If the background in the two images are exactly the same, you can subtract them as you mention in your post.

image1 = imread("/path/to/image1")
image2 = imread("/path/to/image2")
image3 = image1 - image2

Try background subtraction.

Use cv2.subtract(img1,img2) instead of arithmetic operation, as cv2 will take care of negative values.

@dvigneshwr's answer does a subtraction where the resulting negative values are rounded up to 0. @Taha Anwar M-Holmes' answer preserves the negatives but changes the datatype of the resulting array so its no longer a conventional image type.

For those wanting to identify a foreground from a background image based on the absolute difference in values and return an array of the same data type as the inputs (that's how I ended up here), use absdiff.

Assuming the arrays are the same width and height...

import cv2 as cv

image3 = cv.absdiff(image1, image2)

Its worth noting that the OP did not provide any details wrt to the images being subtracted here... depending on what the contents of the images are, all of these approaches may answer the OP's question.