For the Paint method you have the option of setting source and destination rectangles. The source rectangles are in image coordinates and the destination rectangles are in display coordinates (TopLeft). If the image is not in TopLeft view perspective, then the source rectangle is in the image's view perspective.
It is easier to calculate the source rectangle in terms of the display rectangle and then convert it to the image's view perspective using RectangleToImage as follows:
//calculate the rcSrc in TopLeft coordinates
Rectangle rcSrc = new Rectangle(0, 0, 100, 100);
Rectangle rcImage = srcImage.RectangleToImage(RasterViewPerspective.TopLeft, rcSrc);
Medical Web Viewer .NET