我该如何制作自定义图像裁剪

I am new in flex. i'm working with image processing system.Here i try to explain my problem. One Image is display in a image container.I want to crop that image.So when i click the crop button a rectangle box will show in the middle of image.This rectangle will be customized by the user with mouse.When user select his image area for crop just press button and click button the image will be cropped.Please help me for this regard with tutorials or link or source code.I am new in flex. i'm working with image proces