Let us assume the user has selected a window with a chess game running in it. They can draw/markup on the screen as an overlay. If it is using a local app and not a website then they can save the screen capture, but if they are on a web browser and not on an approved website, they may not save the screen capture. The content of the window can be anything and the application can be anything. The key is wether or not they are on a website that is authorised to be "copied" by "this application".
So, yes, I am fully aware that the user can copy (screen capture) the content outside of this application. This is a separate matter.
The intention of this application is to allow the user to download the application on any platform, run it, select any window that is running an application, allow for markup in that window. However, there is a restriction for saving. The user will not be able to save the content based upon the fact the are in a browser and not on approved websites.