C++ Place an image on top of another image in a certain location

I'm looking for a way to place on image on top of another image at a set location.

I have been able to place images on top of each other using cv::addWeighted but when I searched for this particular problem, there wasn't any posts that I could find relating to C++.

Quick Example:

200x200 Red Square & 100x100 Blue Square

&

Blue Square on the Red Square at 70x70 (From top left corner Pixel of Blue Square)