Why would imcrop be the tool to use here, allowing you to crop an elliptical region? imcrop uses a rectangular crop. There are no alternatives in imcrop to let you use a general elliptical region. You will need to write your own crop tool.
But first, you need to decide what it means to crop an image to an elliptical region, since this makes no sense at all. A cropped image is still an image. An image is a rectangular array of pixels. So an elliptical region means you MUST decide what happens to the pixels that lie outside of the ellipse. Until you do that, cropping to an ellipse makes no sense.
