Dynamically insert an image into another image using Python

I am working on a project to create product mockups.
I need a python script which will do the following
1) Take the url of an image file (this file will be in amazon s3 bucket)
2) Overlay this image into another image which will also be present in S3 bucket
3) Write the combined image to an S3 bucket. The final image will be prefixed with final_

I will provide all credentials to the AWS account and will need a script which I can run locally on my computer to do the above.

This project is going to be implemented in multiple phases with each phase being its own separate project and budget.