How do I retrieve a file that's saved to the File Manager?

I am trying to screenshot an element when my user pushes a button and have the image saved to the File Manager. I have that part down and working.

But then what I want to do next is use dynamic data for an image on my page that shows this screenshot that was just taken. So basically I need to find a way to point that image to the file in the File Manager.

Does anyone know how I can do this?