ScreenCapture processing example based on the solution from https://github.com/onformative/ScreenCapturer/issues/2#issuecomment-59645559

SimpleScreenCapture.pde

import java.awt.Robot;
import java.awt.Rectangle;
import java.awt.AWTException;

class SimpleScreenCapture {
  
  Robot robot;
  PImage screenshot;

  SimpleScreenCapture() {
    try {
      robot = new Robot();
    }
    catch (AWTException e) {
      println(e);
    }
  }
  
  PImage get() {
    return this.get(0, 0);
  }
  
  PImage get(int x, int y) {
    return this.get(x, y, width, height);
  }

  PImage get(int x, int y, int w, int h) {
    return new PImage(robot.createScreenCapture(new Rectangle(x, y, w, h)));
  }

}

sketch.pde

SimpleScreenCapture simpleScreenCapture;

void setup() {
  size(600, 400);
  simpleScreenCapture = new SimpleScreenCapture();

}

void draw() {
  image(simpleScreenCapture.get(), 0, 0, width, height);
}