Rendering in CAD

I want to give certain areas in my CAD drawing a material background, but when I try to create a view, it only allows me to create a square, and I need specific boundaries. Any recommendations?
Thanks!

You are creating a square to indicate the size of the image and then clicking an internal point and it will copy the image in the area even if its not a square shape. You can turn off the image border by typing in ‘IMAGEFRAME’ and set it to 0