You show it to the proctor using your webcam. That is all you need to do.
From the FAQ:
One form of government issued photo identification (i.e. driver's license, passport). Any international passport or government issued form of identification must contain Western (English) characters. You will be required to provide a means of photo identification before the exam can be launched. If acceptable proof of identification is not provided to the proctor prior to the exam, you will be refused entry to the exam. You must also consent to having your photo taken. The ID will be used for identity verification only and will not be stored. The proctor cannot release the exam to you until identification has been successfully verified and you have agreed to the terms and conditions of the exam. No refund or rescheduling is provided when an exam cannot be started due to failure to provide proper identification.