How to make object rectangular shape?

I'm trying to segment a card which is rectangular. Due to noise, somtime the segmentation is not perfect but almost understandable. How to make this shape rectangular?

[Image Analyst]

Rather than take a horrible segmentation and try to turn it (some amorphous blob) into a rectangle, it would be better to just improve your segmentation. And we can't give advice on that without your original image. Please attach it.