How to capture dirty parts of screen in java?

Question

I am developing RDP Application. Where server has to send the dirty parts of the screen and client has to update that part of image. I am able to send the total screen of desktop using Robot class as

BufferedImage bufferedImage = robot.createScreenCapture(new Rectangle(0,0,Toolkit.getDefaultToolkit().getScreenSize().width,Toolkit.getDefaultToolkit().getScreenSize().height));

If I want to send dirty parts of screen to client, then how to identify the dirty region of desktop screen and capture that screen.

Could please tell me the procedure to identify the dirty regions of screen in java.