Capture Window and Save to File

Windows Form App using Visual Studio 2015 (c#). Looking for a set of methods that will draw a rectangular around the visual window element when the mouse cursor is over any running windows application, if they click the mouse the program will take a screen shot of that window and save it to a file. It should work on both high and normal dpi displays and multiple monitors. No need to track across multiple monitors (ie one app that spans two monitors). You can assume the running application will be on one monitor only. This is not a full application so you can use a starter windows form project, you don't need to customize it or do any ui work beyond the mouse hover part listed above. The image capture should not slow down the user experience. The output of the click just needs to be a simple image file on click, any format in a folder specified in the [login to view URL] along with internally storing the coordinates of the application in a variable that I can review and test.