Screen overlay with Python, paint over an active window with background python script

I'm writing a python scrip开发者_JS百科t that runs in the background and takes screenshots of another application that is active. Then it analyses the screenshots and now it should overlay a certain image over the active app or the screen. I still need to be able to make mouse and keyboard inputs in the active app.

So I need a way to overlay/paint on another window or on the screen, and still keep the other window the active window so that I can make inputs.

I would prefer to do that with python in Mac OS, but if it isn't possible, other languages and even Windows (if really necessary) would also be ok.

Can anybody help me?

Thanks in advance!

http://www.michaelfogleman.com/2009/12/drawing-on-the-windows-desktop-using-python-and-wxpython/

Seems to do what you want, but is windows only, as are some other answers to similar questions here on stackoverflow