How to create a UIImage programmatically with contents

I'm trying to create a UIImage with some contents in it. In my app, the user will be able to see an image by tapping on different things, and the parts of the image they change would be based on what they tap. I'm doing this by layering UIImages on top of each other. How would I be able to create a UIImage (for the user to export) that takes the same method, by layering images on top of each other? Thanks :)