Thanks,
Those pre-loaded shapes don't work for me, I need to design my own shape with specific outline shape and dimensions, I know people use Adobe illustrator and photoshop but I'm not willing to buy those software since I don't do a lot of design stuff, I just want basic application to shape up the picture to avoid wasting ink on rectangular printouts.

My next option is probably edit the artwork in paint to white out all other parts of the rectangle that are not part of the artwork and hopefully when the print software sees white it prints nothing, and I believe there is a manual cut out feature in Paint, But all these manual processes take time.