The only ways to do so are:
1. physically activate the webcam yourself and hope they don't notice
2. infilitrate their PC with some form of remote control virus (Trojan). Highly unethical, needless to say
Hide in her closet..
yes but i dnt know
There is no way of knowing if someone visits your Twitter.
Sure but you if you do not know the other person...you view at your own risk
View the persons system settings or ask them to join you for a chat on a program which detects the users webcam and tells you if they have one. For example skype. However most if not all webcam clients have settings that allow a user to hide their webcam from being detected by other people.
You don't.
It only costs money to view someone's webcam on random websites that are promiscuous. If you are webcamming with a friend it should be free.
to see or to view one's image
eyespyfx
You can easily view all your contacts in Gmail. Over the compose button there is a text called Gmail. Click it and you'll get the contacts menu.
If you can not view your webcam, it may be because its software drivers are not properly installed. You can check their status/re-install them using Windows Device Manager.
If the account is not protected then you can view it without anyone knowing.