Roi (region of interest) of an image
mask=imroi(image[,type_of_mask,option])
The function allows the user to select a Region of Interest (ROI) in an image ALREADY DISPLAYED, and returns the corresponding binary matrix.
The mask is working with any of binary, gray or color images.
With the ellipse selection, you draw the rectangle in which the ellipse is drawn.
To generate much more complex ROI's, you can use the Gimp (GNU Image Manipulation Program) [www.gimp.org], although of course this is not an integrated solution.
http://siptoolbox.sourceforge.net