'Declaration

Public ReadOnly Property ChangedRectOnSourceImage As System.Drawing.Rectangle

public System.Drawing.Rectangle ChangedRectOnSourceImage { get; }

public: __property System.Drawing.Rectangle* get_ChangedRectOnSourceImage();

public:
property System.Drawing.Rectangle^ ChangedRectOnSourceImage {
   System.Drawing.Rectangle^ get();
}

Empty rectangle (Rectangle.Empty) - memory for image is allocated and image is blank at the moment, customer can change the image, for example, draw background on the image;
Not empty rectangle - image region which was changed (rendered).