I think that is already possible using the
jAWTRobotClass
I checked this and it seems we have to capture the whole screen, then show the captured screen image in a full screen form, draw rect of mouse dragged, cut that image and show in mainform - we have to deal with how to draw mouse dragged rectangle in transparent area issue.
Or use the method I mentioned: make a full screen mainform with alpha = 0.1, interact with mouse dragging in mainform to get rect, hide mainform, use robot to capture whole screen and cut the image in rect.
Maybe I am thinking in a complicated way and there is a simple solution...