At first I thought the title suggested that you can game the system to mark you as verified.
Using a header image is just tricking the user, not the system. I guess that's the end goal, but I didn't see it as creative as I had hoped.
Twitter does not make it convenient to report accounts that are impersonating someone. Moreover it should be fairly easy for them to run a check on the background image to catch for violations of 'verified' user.