I need to implement the crop functionality same as picasa have. When you double click any image in picasa library, an ImageEditor opens. In that image editor, there is functionality of images croping. So I just want to provide crop selection area in same fashion, picasa doing. Like when we select a image area for crop, all image goes dark, and selection rectangle remains glowing.. I inherited QGraphicsView and using QRubberBand for selection rectangle.
Can somebody tell me how I can achieve that. I am attaching screen shots of picasa stuff.

this is image url
http://lh4.ggpht.com/yogeshgokul/SGD.../s400/crop.JPG