title: Crop irregular shape into a rectangle
body: <p>I'm working on a project that requires the user to select and object from an image. I'm currently doing this by allowing the user to draw a rectangle around the object (the object that needs selecting is always rectangular) I can then crop the selected area. The issue is that in the image the object may not be viewed from a birds eye view and therefore in the image it is not perfectly rectangular.
  I have now changed it so the user draws around the objects using lines which works fine but I'm unsure how to crop this irregular shape and then stretch it to fill a rectangle (as I need it to be a perfect rectangle but not have any of the background) some guidance on techniques and where to look would be great. I'm currently using aforge to crop my image.</p>
  
  <p>Thank you</p>