Crop image with edge detection

Hello, I want to extract a sheetmetal-edge so that the rest of the picture is completely white. The edge is not completely rectangular it has a burr on both sides, how can I extract the sheetmetal? Attached is the image.

[Prajwala TM]

We want to do something very similar. We want to crop a leaf from its background. Did you figure out how to do yours? Attached is the image.

[Rik]

Have a read here and here. It will greatly improve your chances of getting an answer. Show what you have tried, then we can more easily help you.